Is there a way to upgrade from v0.9.1.74 to the most recent version without losing all the blocks? Last time i did it claimed the blockchains are corrupted. Or is that update without problems on that level?
You should be able to upgrade to 0.9.1.75 from 0.9.1.74 without any problems. If you want to be really sure, make a security backup of the whole working directory beforehand (just copy the whole Credits dir and name the copy Credits_backup).