The pump is in the gas tank. I've never removed mine, or on a Subaru, but on other cars I have seen the gas lines and tank are under some sort of access hatch on the floor.
Usually, it's held down with 3-4 screws, remove them, remove the hatch, and then you can see down to the gas tank. You'll see the gas lines going in and out, as well as the wires to the pump. It will also have a removable hatch on the gas tank. Be sure they lines are not pressurized, remove them, then remove the hatch.
No smoking or making sparks!
Once you get the thing out, the pump is mounted inside the gas tank hatch, on an arm. You should be able to figure out how to remove it, if needed.