Max_user_connections for MySQL

[romow]

Hi,
I'm running a forum.
Often I got this error from my forum:

mySQL error: 1203
User xxxxxx has already more than 'max_user_connections' active connections
Query:

and the forum becomes inaccessible briefly.

Can I adjust the max_user_connections somehow?
I checked MyPhPAdmin, but couldn't find any related info..
Thanks for your help!