Loosen the intercooler to throttle body hose. There are 2 8mm hose clamps holding it on. We had success only loosening the rear-most clamp.

Loosen the turbo to intercooler hose. There is a single 8mm hose clamp holding just visible under the left side of the intercooler

Slide the rubber PCV hoses off of the ends of the metal lines running along the front of the intercooler. There are 2 on the left side and 1 on the right.

Remove the recirculation valve (blow off valve) by removing the 2 x 12mm bolts that hold it to the intercooler.

The intercooler blow off valve gasket part number is 21896AA072 for (2002-2005 Impreza WRX, (EJ205), 2004-2014 Impreza STI, 2015-2018 WRX STI)

Remove the 2 x 12mm intercooler mount bolts at each end of the intercooler.

Remove the right side intercooler bracket.

This is optional, but it will make removal and installation a little easier. It's just 2 x 12mm bolts.

Now the intercooler will wiggle out.

Wiggle the intercooler away from the throttle body and turbo simultaneously. I found mine slide right out by wiggling it back toward the firewall and a little to the right at the same time.