The in-app 'update' button does not work very well, it's recommended that you disregard the update button and download a fresh install.
There is a new command in siac for merging wallets. If you have coins in multiple wallets, you can use the merge wallets command to load them all at once. You will have to restart siad to see the new combined balance.
Whats the difference between Sia and Sia-UI ? which one should I use ?