There is an update available. (I am on openSUSE 13.1 64 bit)

But the update hangs for ever. (I also tried to update through yast, but then the same thing happens)

It says updating packages LMMS
Installing package LMMS, and then nothing.
Progress bar does not show progress, and waiting for hours does not help either.

How can I find out more about what the problem is ?

LMMS comes from the packman repo.

https://lmms.io/