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).
That means with this version i can simply overwrite the old files with the new ones after i made the backups you mentioned? It will not find a corrupted blockchain afterwards? I think i already had to recover the blockchain from the torrent file around 3 or 4 times.

Would like to avoid that in the future.