I bought a linode 2048 3 weeks ago. though one of my friend's account.
now I decide to pay by myself, by my own account(which not reg yet.)
can you transfer the linode directly to my account so I don't need to move the data and remap the domain ip?

Yep, we can do that for you. What you'll want to do is open a new account, which will require you to add a Linode when creating the account. Adding a 512 monthly will be you cheapest option when opening the account, you can remove the unneeded Linode for service credit as soon as the account is open.

Once both accounts are open you'll want to open a support ticket from each account requesting/authorizing the transfer. Once we have both tickets we'll get that Linode moved right over for you.

thanks, now next question:
how will you charge me , if I paid for 2 year,but decide to upgrade after 3 month?
ex:
I paid 2 yrs 2048, it's 79.95*24*0.85= 1630.98

and 3 month later, I decided to upgrade to Linode 4GB, how much shall I pay, and how will u caculate the bill cycle. restart 2 years, or follow the old ending day?

plus: I don't see your price for extra storage.

The price for extra storage is (or was, last I looked) $2 per gig. It's far cheaper to upgrade your linode, in most cases.