There is not much to do.
Shutdown the PC. Start the PC, insert your windows media, and boot from it. (You might need to get in BIOS Setup and set boot sequence so it boots from CD or USB before trying to boot from hard drive.) You should see a screen saying Click any key to boot from CD, just click any key before it boots from hard drive. Eventually you get to a screen with
UPGRADE...
or
CUSTOM INSTALL....
Pick Custom. This will install a fresh Windows. You will see a screen that asks which drive to install to. Click Advanced.
Click delete partition on all partitions on the hard drive. Some may not delete but eventually you should end up with one or two empty partitions. Click Format. Click Install. Windows will take it from there, installing itself and leaving you a clean system. Easy peasy.
Old data and software is still there, because you did not wipe it, but no harm. Over time you will write over the old data. I see no need to wipe the disk. That takes time, and the old data harms nothing. It will get clobbered in normal use, just forget about it. Unless you work in financial or government agencies, it's not required to wipe the disk.
If you really want to wipe the disk, there are many programs that do it. I use CCleaner, a free and very useful garbage collector program that has a partition wipe capability. But if you use it on your Windows partition, you'll just have to reinstall Windows all over again. Again, I don't do that, but if you really want to, wipe away.