It is easier to delete the existing printer and add it again, as if you were doing that for the first time. Perhaps the following will jog your memory.
Generally speaking, for IP printers connected via Ethernet or wirelessly, you go to System Preferences > Print & Scan, and click the + (plus) button. Most of the time the printer is found automatically.
If that doesn't work, click the IP pane, select "Line Printer Daemon", supply the printer's IP address, the queue name (this is optional unless you are using a print server), the name you would like to give the printer (any human-readable name is acceptable), and its location (optional). For "print using", click "select printer software" and scroll through the list until you find an appropriate driver.
When you are done it ought to look something like this: