I am posting this Q because the answers to similar questions leave me unclear, so please help, if you can.
I have a Dell E521 with AMD Athlon 64 x2 DCP 4200 2.20 GHz, 32G RAM and with 2 HDD, C: and D:, running Windows 7 Professional SP1.
When I added the 2nd HDD I clean-installed Windows 7 to that drive (now C

because I did not want to wipe any files. I installed the 32-bit (mistakenly, I am now told) instead of the 64-bit. Vista OS is still on the old drive (D

and there are lots of new files and programs on the new drive (C

which I want to keep.
I understand that I must do a clean-install of the 64 bit Windows 7 but do not understand whether this will wipe my files on the C; drive. I have no knowledge of partions and have not, to my knowledge, created any.
So my Q is:
How do I move fom Windows 7 32-bit to Windows 7 64-bit without losing programs or data?
many thanks to whoever can give me a clear, easy-to-follow answer.
Much obliged