Sleeparu

Okay... I asked my Subaru dealership this and they were clueless, so I'm hoping someone out there can help me with this! I have a 155hp 1996 Subaru Legacy GT that I'm planning on upgrading... lots of mags with how-tos on the Impreza 2.5RS that I have lots f info... the one thing that nobody can tell me is this: What did Subaru change from the 1996 to 1997 model year to jack the horsepower rating up by 10hp? Can I do this to my engine with relative ease? Thanks all for help!