There is a good spark plug change DIY in the DIY forum. Getting the coils off is kind of a PITA but doable with the right tools and some patience. Not something you ought to do if you aren't comfortable...
08 E90 | Jet Black / Black | 6MT
Mods: RAC RG63 w/ Pirelli Corsa 255F/285R | Akrapovic Evo Exhaust | OEM Blacklines
Winter Setup: OEM 18s w/ Nokian Hakkapeliita R 245/40-18