Installing windows 7 64 bit on a 32 bit vista

Hello,
I had upgraded my factory installed 64bit vista home premuim to wondows 7 64 bit, last week i had a system failure and it asked e if i wanted to re install the facory settings which i did, in this process it asked me to back up my data, which i did, after this was done, i installed my wondows 7 back in the system but now it did not read the backup file it created.......so at the time i had only a 32 bit vista OS, after i installed i could recover my data from that file which could not be read on windows 7, the problem now is i want to re install windows 7 64 bit .

its not allowing me to do that.

please advice how can i reinstall my windows 7 64 bit from a current vista 32 bit.

thanks

charlston.