You need to purchase a wireless adapter, preferably a PCI type for the PC. You'll need to set up the wireless while wired, then unplug the wired LAN connector and go wireless.
I have a DLink 514 (I know it is old) connected between my DSL modem and my PC so I can use the wifi in the 514. Is it possible to disconnect from my PC and to connect to the wifi with the 514 having no wired PC attached? If needed, I'll upgrade router if later version will do what I'm asking.