yes he is right... youll need a 1/4 inch wratchet with a 6 inch extension and a 10mm socket and a flat blade screwdriver.
top right passenger side use the screwdriver to pop the plastic carpet stay off.... fold the carpet down. The ecu is right there... there is a plastic covering on it. take the covering off and there is a sheild. Take the 4 10mm off the sheild around the 4 caorners... then u see the ecu with 3 10mm nuts, take them off and then the 3 wiring harnesses and out comes the ecu... should take all of 5-10 mins to take out.
I have a DSM. Im a Subaru Technician. I like to check out the site to help a bit with diagnosis and to learn about the "WRX perfrormance" end of the stick.