Hi. Welcome to Jabref!
Completely new reference types are saved in the bib file (at the end, in form of a JabRef-comment tag) and when you open this file in a other Jabref instance you will be asked to import the new type.
If you modify an existing type (e.g. add a file to the standard article class), then the procedure is slightly different. Instead of serializing the modified entry type in the bib file, Jabref remembers it in the preferences (stored in the registry by default). So in this case you can export your preferences on PC 1 after editing the entry types and then import these changes on PC 2.