Hi,
Don't actually need to change anything. v4 works with masterpages out-of-the-box. Nothing changes, so you can just continue as you are now. It's different if you've downloaded v3.x - I don't know from your post -, then you'd need to change quite a lot to be able to work with templates as designed in v3.
If you need help moving content, just ask here and people will help you out the best they can.
Hope that helps.
Regards,
/Dirk
level 1 & 2 certified - umbraco MVP 2008/2009 - umbraco blog at
netaddicts.be - working on an integrated forum4umbraco