
Merging libraries from different user accounts is done much like any other merge, but is complicated by the fact that by default, one user account does not have permission to access another user account's files. The easiest way around this is to make a copy of one user's library (let's call them user A) to another location where the other user (whom we'll call user B) can have access to it. The best place to copy the library to is an external hard drive, since the system by default ignores permissions on external drives altogether. If an external drive isn't available, you can instead copy it to a shared location, such as the Shared folder located inside the Users folder on your internal hard drive.
So, to summarize the steps: