[PROBLEM] How to increase swap size

[LeoSum]

Hi,
I am running xbian on my model b raspberry, which is working fine. However I installed owncloud 6 on the same machine, using nginx and MySQL. The webinterface is awfully slow, much slower than what I see others are experiencing from youtube videos that show it running on a raspberry using raspbian.
The setup process from tutorials worked on xbian too. The only thing I couldn't acchieve was increasing the swap file to the recommended size of 1024MB which supposedly increases performance.

How do I do that in xbian?

Are there other options to speed up owncloud a bit?

Regards
Leo