See this guide on a step by step clean install. Just delete all partitions and then press next. Windows 7 will automatically partition and format the drive.
If this is an upgrade disk and not a full install disk you can see this guide on doing a clean install using an upgrade disk.
Edit: If you cannot get to the Window that allows you to delete the partitions then at this Window press Shift + F10. This will open a command prompt window. Type the following
diskpart Will open the diskpart command window
select disk X Where X is the number associated with the hard drive you will be installing Windows to. If you only have one hard disk it will be disk 0.
clean This will delete all partitions
exit Exits out of diskpart
exit Exits out of command prompt
Press Next to continue the install.
Edited by JohnC_21, 09 July 2016 - 08:17 AM.