Is there a way to disable automatic download update?

Not really unless you switch off the WifI and don't connected to the phone and never use Garmin Express.

There are a host of fixes in the beta release 3.55 that I would recommend upgrading to it.

Thanks for the reply. I can easily do without ever connecting to garmin express, but NOT uploading activities through wifi is too big a feature to miss. That's why I believe being able to choose not to automatically download software updates while connected to wifi will be a good feature to have. Version 3.20 has been working flawlessly for me so I really see no reason to update and risk having to go through any possible frustrations. But I have to say I don't use navigation, and I don't ride with my phone connected, and I have my sensors connected through ANT+.

In short:

agree uploading good, auto downloading bad. downloading more successful when garmin connect is linked via phone. also for big files, like map updates, the only way is Express.

More ramble

(However, I have found that after a wired update, lots of things need re-setting on the unit; sometimes zones, sometimes segments go quirky, sometimes maps. aaaargh settles down after re-writing and doing some wireless bluetooth updates) wish garmin would talk to apple sometimes who seem to manage transition smoothly.

I agree concerning update. I normally have to re-set up my data fields after an upgrade. But this time I've had to spent 30 min to an hour restting all my screens and data field. Wish this could be fixed. Frustrating is not a strong enough word. 

Check out my post from two years ago. I'm still happily on firmware 7.1 https://forums.garmin.com/sports-fitness/cycling/f/edge-830/267916/edge-8-00-gcd-update-file-available/1284278#1284278