Step 1: Open your gallery:
If you cannot open your gallery due to a limited space error, then temporarily uninstall large apps until you can reclaim that space.
Step 2: Open gallery settings by pressing the left capacitive button on your phone and select Settings:
Step 3: Select any/all email account(s) associated with Picasa Web Albums which you'd like to remove:
Removing these albums does not delete your pictures, it only unsyncs the album from your phone. You want to do this because it's the Picasa Web Albums which are generating the massive thumbnail files.
Step 4: Uncheck Picasa Web Albums:
Step 5: Go to your home screen and open Settings:
Step 6: Select Application Manager:
Step 7: Clear data:
Step 8 [optional] : Use your preferred file manager app to confirm you've freed up internal SD card space:
Remember to reinstall any apps you may have temporarily uninstalled in Step 1!
I hope this helps!