I uninstalled it completely and then installed new version from scratch. You have to manually delete a lot of files. Here is the link to a guide http://wiki.gridcoin.us/Wallet_upgrade . Then you have to re-download all blocks and let it sync. Takes about 3-4 hours.
Good luck, I was really pissed by the end of it.
Some of tips not covered in the guide:
-if downloading blocks gets stuck at 99%, don't worry, it's normal, just tough it out.
- after downloading it still has to resync a good number of blocks on it's own, monitor it and if it gets stuck more than 5 minutes on the same block, restart the wallet. It may take 4 or 5 restarts till it is fully synchronized.
- persuade yourself it is for the science and you had nothing better to do with your time:)
RE: Results of the contest "Tell me what to buy right now! [23] GRIDCOIN (GRC) , BITSHARES (BTS) and EOS (EOS)" by toofasteddie