Press the pins out of the cranks. (You can use a large "C" clamp and a large socket to do the work) Back off the fixing bolt and cups (there's a wrench for that) than clean things up, add new bearings and replace the grease. Setting the BB will be a little fun until you get feel if it. Sheldon Browns site has more than enough information to walk you through it. It's a fun job for a rainy evening.