I am unable to upgrade my Edge Explore from 4.30 to 4.60. The device performs upgrade validation (0-100%), turns the device off and does not turn it on. When I do it manually after some time the firmware is still 4.30.
You might try to install the update through the menu: System / About / Software Update
If no update available remove the file GUPDATE.GSC from the folder ..\Garmin and let the Explore sync again by Garmin Express (latest Windows version is 22.214.171.124
If this does not resolve your issue, then do a full factory reset of the device (all settings are lost!!) and try again using Garmin Express.
If you are using Apple I don't know if there are known issues causing troubles with updating firmware.
In my case the update worked without issues (Windows 10 64bit, GE 126.96.36.199
I disabled GPS and phone connection, removed the GUPDATE.GSC from the folder ..\Garmin, synced again via Garmin Connect (Windows 7) and upon powering up the device asked for upgrade. I clicked Upgrade now and it worked.
If I had to factory reset this rubbishy device in order to do the upgrade I'd have sold it.
This is very intuitive, Garmin (turning off phone connection), have you thought about fixing it?