Easiest way is to just stop logging in. If you're tired of getting notifications, add it to your spam list.
I ran across a few threads awhile back where some guy had gotten pissed off at the forum and had systematically deleted all of the content of each of his (many, many) posts. Some of that information really would have been helpful.
Just leave it be. It's not like you're getting charged.
Blue-ish 2006 2.4, Werks stage 1 turbo, Borla cat-back, DDM braces, Spec aluminum flywheel, Spec stage 2 clutch, Werks aluminum radiator, some gauges, RKSport hood, Morimoto FX-Rs, GReddy Profec, Norm's fenders
'07 GXP, RPM Stage 2, Solocatless downpipe, TCE Wilwood 6 piston front brakes, 4-piston rears , Stainless brake lines, slotted/drilled rotors, BC Racing BR coilovers, Performance Autowerks intercooler, DDMWorks CAI, charge pipes and braces