Best way to clear or wipe your hard drive?

[Boise40]

I plan to sell my old desktop PC and see if I could get enough for a new desktop or laptop. However, it always seem to be a challenge for me to clear or wipe my hard drive. I'm usually good about putting a computer together and taking it apart. It just seems like I can never accomplish this goal of clearing/wiping my hard drive. I don't want to hand my computer over to a professional and have them charge me for their service. I usually like to work on something and learn for myself. Anyways, could anyone give me some advice or tips? Thanks in advance for any help

[dexterjrh]

I used a secure delete and worked for me

Download from the internet it was free, but worked