License and adopting software

[blubee blubeeme]

I like some old software that's <= GPL2 but it seems like the original
developer is not and have not done any work on the software sine mid 2000.

I'd like to pick up the project, fix bugs BUT i'd like to migrate from GPL
to BSD license.

How does one go about doing that? I have seen the GPL code but it could be
re-written how would that affect me re-writing the code with a new copy
center license?