Wiping a hard drive computer / installing new windows

If you just want to wipe the hard drive you can use Ubuntu boot able flash drive and full format the hard drive.

If you need to install windows:

1-create another partition.

2- move important files to the new partition.

3- full format current windows drive in ubuntu

4- delete the current windows partition and reinstall windows

5- Show the old file to client and full format the partition after they coppied what they need.