Why can't I change the isolation levels of my connection in MySQL?
You need to try
SET tx_isolation = 'READ-UNCOMMITTED';

or
SET SESSION tx_isolation = 'READ-UNCOMMITTED';

You could also declare it at the start of the transaction
SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;

Give it a Try !!!
CAVEAT
Please note that you misspelled READ-UNCOMMITED (Missing T). It should be READ-UNCOMMITTED
You cannot change tx_isolation in the INFORMATION_SCHEMA database because it is an in-memory read-only database.