You can go to
this site and download EasyBCD 2.0.2
This will allow you to specify what OS you want boot into by default, you can also remove the entry for vista. After that you can go into Disk Management and delete the partition holding Vista (be sure to back up and data you want before doing so). After you delete that partition you can remake it into another data partition or expand your Windows 7 one into that unused space.