Combining Memberships of 2 Sites

[KMANJD01]

Hello, I would like to merge the memberships of my 2 sites. One of my sites is on the vBulletin system and the other is on WordPress, both hosted on the same domain name as follows: 1st site www.sitename.com, 2nd site www.sitename.com/forum. Can I get information related to this topic? If this is a complex process, can knowledgeable friends get in touch? Note: If I posted this in the wrong place, I apologize. I saw this as the most appropriate location.