- started my "old" viacoin wallet (windows 64 bit)
- unlocked wallet
- exported private keys
- closed wallet
- made backup of wallet.dat
- renamed ...\users\username\appdata\roaming\viacoin
- downloaded Viacoin 0.13.3.1
- installed it and started it up
- now it is syncing : waiting
to do
- after wallet is 100% synced: restart wallet
- restart OK? yes, close wallet
- copy "old" wallet.dat to folder ...\users\username\appdata\roaming\viacoin
- start wallet: if funds are there: OK
if not I have to import the private keys.
I guess this is the safest way to update