I assume you're talking about a DB. Flipping it to redo the bottom is biggest pain of the process. Short of getting 3 or 4 guys to help you here is the process I use.

I have several big chunks of cardboard (flattened old boxes from large items) I lay on the garage floor to allow the boat to slide on the cement. I then launch the boat on the the cardboard and remove the anchor nest.

Since I have a center post in my garage I then roll the boat over against the post and then slide the cardboard away from the post until its completely flipped (I also have a peice of cardboard I put against the post so the boat will slide against it).

Once its flipped I them lift each end and support it with a 2x4 resting on cinder blocks. You will need a second set of hands for this part, but its something a wife can easily do.

I have a 16' aluminum DB and I can do this solo. However, if you have a bad back I would recommend getting some guys to help you as its not easy and there is some awkward lifting involved