PSP/Install 6.20 PRO

Download 6.20 PRO-C.
Extract the file.
Copy the contents of the extracted folder into the root of the Memory Stick (ex. PSP -> ms0:\PSP, seplugins -> ms0:\seplugins)
From the XMB (main psp menu), run PROUPDATE from Game - Memory stick.
Press X to install CFW. You have now installed Temporary 6.20 PRO CFW.
To install permanent CFW, run 620 PRO-C Permanent Patch.
Press X to start installation. It will ask you to test the system before installing; Press X.
If there were no problems, run 620 PRO-C Permanent Patch again. Press X to start, but press O to skip test mode.
On the root of your Memory Stick, a vshorig.prx file has been created. Do not ever delete it; you will need this file to uninstall 6.20. Back it up somewhere safe on your computer, in case your memory stick fails.
You have now installed Permanent 6.20 PRO CFW.

To uninstall, run 620 PRO-C Permanent Patch again. Alternatively, fully shut down your PSP and hold O + X + START + SELECT while turning on the PSP. Make sure your vshorig.prx file is on the root of your PSP before uninstalling.