Rollover for Emini and other futures contracts. Switch month code from M to U. Typically you will switch from M6 to U6 on all your contracts by or before 09:30 EST today.

More information about rollovers can be found here:
http://www.deltat1.com/Education/articles/Rollover/rollover.htm

Month code are:
H - March
M - June
U - September
Z - December