So you want to take your server to the next level? There are a lot of old posts about this, and the ones Google likes to show are all missing a crucial detail. There are four variables that contain this data. They are all in the rule_values table. I don't see a page for this, so here it goes.
In this example I'm setting the Max Level to 100; change this value as needed.
1) Open a MySQL Admin tool (Heidi, OmniDB, MySQL Workbench, etc.) and connect to the eqemu database for your server.
2) Run the following SQL Statements:
UPDATE eqemu.rule_values SET rule_value = 100 WHERE rule_name = "Character:MaxLevel"
UPDATE eqemu.rule_values SET value = 100 WHERE rule_name = "Character:MaxExpLevel"
SELECT * FROM rule_values WHERE rule_name = "Character:MaxLevel" OR rule_name = "Character:MaxExpLevel"
You should have 4 records returned. If everything looks correct, proceed to step 4.
4) Restart your server.
Thanks to Akkadius for the clue on multiple variables.