Wii system update question?

I had homebrew on my wii for about 2 months but then I decided to erase it because I wanted a wiiware game. It requires an update, and don;'t know if it will brick my wii. I erased everything that contained homebrew, but don't know what will happen if I update it. I think my wii is at 3.4 and I need it to be 4.2. So anyone know what will happen. (And I don't wanna do format my system because I have like 15 wiiware and VC games and a lot of saves)