It is not uncommon to be able to convert phone lines to Ethernet, but before you get started you need to make sure that the phone lines were originally put in using the right kind of cable and topology (or network design) to be able to be used for Ethernet. Once you are sure the original network was set up in a way suitable for conversion it is simply a process of re terminating all of the cables with the proper connectors and verifying that everything is set up correctly.

Depending on the network there are several ways to find the other end of an Ethernet cable. If you are lucky they will be labeled with some information that can give you a clue as to where to start looking. If you are not so lucky there are still a hand full of tools and techniques that you can use to track down the other end of a cable including your network router, multi-meters, and specialized tools called toners.