Does it's possible to donate in multiple part ?

For example, 5 BTC right now, and 5 BTC later for the 10 BTC total of "Donator" rank. (Same question for the VIP)

And does if a "Donator" want to get "VIP" he just have to send 40 BTC more, or he have to repay 50 BTC in total ?

Thanks in advance.