http://www.lmms.io/forum/viewtopic.php?t=3387
I wish I could help, but I have no answer to this problem.
The only thing I could say, is if you are using windows, try to find the screen resolution option, and change it from there, to something smaller.
Hopefully, one of the other Lmms guys might have an answer.
Or probably, the answer is in that previous post I linked to.