itch.io

In short: don't delete your saves
In long: download new file, move saves over, delete old file

Progress shouldn't disappear when updating in Android, unless you do the uninstall-reinstall technique when updating. That is not how you update something in Android, unless GW's signatures change for every version, for whatever reason.

EDIT: Further confirmation shows that GW does NOT change signatures every version.

And here is how you update GW on Android, if you have an old version:

Step 1: Download the newer version

Step 2: Click on the downloaded file

Step 3: Click the followup "Update" button

Step 4: Wait

Simple as that.