02 Impreza are i believe still bugeyes...so its pretty easy....open hood, undo headlight/parking light connectors, remove the little side trim piece next to the headlight (two clips i believe) (between the grill and the headlight housing),than i think its two 10mm bolts up top and there may be one on the side after you get the trim off.....if your at all mechanically inclined its not that hard at all....if you have any other trouble this link should help you out...i found it a little while ago and has proved very helpful for me....the 02 impreza service manuals....
Impreza Manuals | ken-gilbert.com