DISCLAIMER: I am not an TFS expert, at all.
Besides the normal of modifying the password in service manger, I found a few other things.
Hopefully it’s a VM so you can take a snapshot before you do anything.
Much of this data I got from “How to change the Service Account or Password for Team Foundation Server”
1) SQL reporting services will need to get updated, I believe you can do it through the TFSAdminUtil with the /ra option, or you can run through the Reporting Services Configuration again.
2) You may need to modify service account passwords on IIS Application Pools, such as the “Microsoft Team Foundation Server Application Pool” under Identity update the password, I had to update 3 of my pools.