Memory Low. Upload to Garmin Connect.

You can see your activities on Connect?  If so, it’s telling you the watch memory is full and you need to clear out some activity fit files or remove some watch faces or apps etc.  Connect your watch via the cable to a PC.  Once you do that, open the Garmin folder, then Activities and remove some of the .fit files.  

I'm getting the same message. I deleted the fit files on my computer, and also went into the app to clear activity files. The message keeps popping up on my watch face, it's super annoying!

You probably need to delete any downloaded watch faces and / or apps temporarily as it’s probably trying to download an update to the watch and there isn’t room.  The easiest way is just to connect to express, remove fit files and also anything you’ve downloaded to the watch.  Once the update is done you can re-load them from the app very easily.

There's an answer from Garmin about this.  I think it was not going through Garmin Connect but using Garmin Express.  That did it for me.  It was wonky getting it done, but eventually 'took'.  Be sure and restart the watch after wearing it a few minutes after the update a second time just to be sure you are good to go.

I've been in touch with Garmin support. So far, I've tried everything that's been recommended in this thread so far, and it still hasn't helped. I'm pasting the instructions into here incase they can help someone else:

• Connect the Venu Sq device to the computer and open the Garmin Folder > DATA >FNT
• You'll want to look for and delete the following files - D844800.FNT (Chinese) and D844802.FNT (Korean)
• After the above files are deleted, sync the device again with Garmin Express to download any available software updates. Note that software updates are downloaded in the order of their priority. So even if the “not enough free space” error message is displayed, the most important software updates would have already been downloaded successfully to the device and are pending installation.
• Unplug the device from USB and select “Yes” on the device touchscreen display to allow it to complete the pending software updates.  Once these software updates are completed, there will now be enough free space available for subsequent updates to complete successfully the next time you sync your device.
• Reconnect the device to USB and sync it again with Garmin Express.  Any additional software updates, including the Chinese and Korean language files deleted by the previous step, will be downloaded.
• Unplug the device from USB one final time and select “Yes” on the device touchscreen display to allow it to complete the pending software updates.  All available software updates will now have been applied, along with successfully reloading the Chinese and Korean fonts.

I've now moved on to copying the entire "GARMIN" folder from my watch to my desktop and sending a .zip file to product support for further help. I'll make sure to keep this up to date with my findings. Might be time for a new watch though, I've only had this one for 3 months and it's a hassle.

It worked for me! Thank you!!! This message (memory low) was appearing in Gamin Express while syncing.

I am in exactly the same position you are in - memory low then memory full - the watch doesn't even show the time any more and is completely useless.  I have had my watch only a few months as well and have deleted my activities from the watch on my laptop regularly and have uploaded to connect every day.... I have now deleted the two files showing above and will see what happens next. Thanks for posting.  Can't say I've enjoyed my experience with this watch at all.

I am coping a post from CindiL that I found explicitly listed for Venu Sq (which I have); I am sure it applies to other models.

"Are you seeing current information when you open up Connect?  Do you see you latest activities?  If so, you are syncing, it’s just that your watch’s memory is full.  If you are seeing current activities in Connect then you can remove old activity files *.fit from the watch by connecting it with the charging cable to a pc and removing old .fit files under the activity folder.  It normally should do this on it’s own but once this has happened to me before also.

 You can also remove some watch faces and/or content if you have downloaded those from the Connect IQ store to free up memory."

I would add that you do not need to download any software to do this. Use the charging cable to connect your watch to a PC. Find the device in the PC's "folders". Once opened there, open "Activities". Delete files that have dates as part of the names or ".fit" files, which is probably everything. 

Of note, this started happening while I was out hiking for a week. The annoying popup reminder became more frequent as the month went on. 

I've just been getting similar message. I went into setting on watch and there was an option to delete all activities. I did this after first ensuring all were synced to garmin connect app. They have now all gone from watch but are still on app and as yet message has not reappeared