If it's before 5:45pm, you should park in the San Jacinto Garage (formerly known as PG1) which you can find here.
To get from the garage to ACE, walk south on San Jacinto to 24th, then west on 24th. ACE is on your left, about 300' from San Jacinto and 24th. (Map of the ACE region is here.)
Parking rates - basically 3$ per hour, with an $18 max.
If it's after 5:45pm, parking on campus is open, except for a few marked spots.