turn off the computer and take the side panel off the case. Plug the second drive in and use a program like Marcium reflect to clone your 250GB drive to the 1TB drive ( make sure you get the 100mb boot manager partition at the beginning )
Once you have cloned the drive turn off the computer and replace the 250GB drive with the 1TB and boot back up, if everything went right you should boot into windows. If it doesnt boot then put the 250GB back in and try again.
IF everything boots just fine off the 1TB drive you will have to go into disc management and allocate the extra 750GB to your C drive giving you back the full 1tb drive.