How do I change a Printer on my iPhone 15 Plus?

I'm not sure I understand your question. Typically, your iPhone will only give you the option to print to a printer, which is AirPrint, which it sees connected to the same network as your iPhone is connected to.

Printers are not installed on iPhone and therefore there is nothing to uninstall. Instead, iPhone listens on your network for AirPrint compatible printers to announce that they are available to use. If you are not seeing the correct printers on your network try the following steps:

1. Restart your iPhone
2. Restart your printer, then ensure that it is joined to the same network as your iPhone
3. Restart your Router/Gateway
4. Read: About AirPrint - Apple Support
5. Read: Use AirPrint to print from your iPhone or iPad - Apple Support
6. If you are still having issues, visit the support site for your printer and see if there is a new "firmware" available for your printer