Run this mysql query:
Code:
update variables set value = X where varname = 'EXPMod';
X is the xp value you want. I think 1 is default so anywhere from .1 to .9 would lower it.
If you don't have an EXPMod variable this will insert it:
Code:
insert into `variables` values ('EXPMod', '1', 'Experience multipler. Increase to increase exp rate', '20050610185738');