Hi Veysel
Both way it's a big effort as things are completely different in 7.2 so whether its UPGRADE or fresh/new install is always more of challenging/consulting question for any specific customer
however general recommendation from SAP are always plan an upgrade if you are using various functionalities of it and do fresh install only incase it is not used at all or little purpose like EWA etc.
Further, as you have mentioned you would like to migrate PROJECT with DOC to newer version this is definitely not possible and this is the specific reason SAP has given CONTENT ACTIVATION to get transfer project/solution into NEW SOLUTION DOCUMENTATION
Thus, I would request you to please go through below wiki to get more details about content activation process
SAP Solution Manager 7.2 Content Activation - Solution Manager - SCN Wiki
it has pretty good documentation on how you can start preparing today as well.
Hope it helps.
thanks
Prakhar
