I want to install a used power supply to my computer. What tools do I need to get the job done?

My power supply is dying and I need another one in order to search for jobs. I want to save money by buying a used power supply for my desktop PC and installing it myself. So far I only know how to unscrew the bolts that hold the metal cover. The wires inside need different tools to access.
Update: The store I am going to says that the used power supply was refurbished. If I can get one to two more years out of my old computer then I am up for it.
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