How to update my Early 2015 MacBook Pro to Ventura?

Sorry, you cannot upgrade it to Ventura. The last possible upgrade is Monterey.

See the following from Identify your MacBook Pro model - Apple Support

MacBook Pro (Retina, 13-inch, Early 2015)

Model Identifier: MacBookPro12,1

Part Numbers: MF839xx/A, MF840xx/A, MF841xx/A, MF843xx/A

Newest compatible operating system: macOS Monterey

To upgrade to Monterey (if not already done), see: How to download macOS - Apple Support

Building on previous posting above

If the user whats the latest and greatest versions of macOS  all is not lost.

If the user wishes to explore the Apple Trade-In  Process where the Value of the exiting device could be used against the cost of a new Apple Computer.

Or Shop Refurbished Apple computers at an Apple Reduced Cost

Have used both previously and have been satisfied each time.