You will need a a custom (advanced) install. Make sure that the partition you install to is the old Ubuntu partition - do not accidentally overwrite the Windows 8 partition (you can check this by looking at the different sizes of the two partitions. Provided that you take care to do this you should have no problems with files on the Windows 8 drive as none of them should be affected. Even so, I would copy any important files to an external drive to be sure of preserving them. You should also have a set of recovery disks burned to recover your Windows 8 installation. If your pc came with Windows 8 pre-installed then it should have a utility program to burn a set of recovery disks. If it was not pre-installed then you should have the Windows 8 disks need to re-install it in case of a problem.