It will honestly be cheeper and easier just to forget the cables going through the walls and go down and pick up some new cables. Take this opportunity to wire to CAT6 to take advantage of higher speeds as you update other parts of your network infrastructure.

Are you running the cabling to a patch panel? Or straight into a switch? By "muli-ethernet jack " I assume you mean like a quad box or something similar.

Regardless, if you are doing the cabling yourself keep in mind that the specifications for installing cat6 cabling are much less forgiving than those of cat5 or cat5e, for things like how much shielding should be removed for the install or how many twists can be undone (Shorthand is: As little as possible). If you don't have one, you should definitely rent a tester that is able to verify the install (i.e. meets specifications) since this can save you a lot of headaches down the road.

That being said, cat6 is definitely the way to go to future proof things. This site has a nice informational write up:

www.broadbandutopia.com/caandcaco.html

As others have said, if this is to save money for your company, do not bother. Just get new cabling installed at the new places.

Unless these are special cables, aka, not cat 5 patch cables, but you'll need to come back with specifc info if you want extra help.

If you want a bit of cable for home, another matter.

If the cable goes from the back of a patch to the back of the wall plug, just unscrew the wall plate/socket and cut the cable with side cutters. Then, depending on length, you might be able to just pull it back at the server room panel, where you cut if off the back of the server room patch panel. The worst case is you need a ladder and have to pop a ceiling tile (use back of hands), pull it up the wall cavity, then pop ceiling tiles every through metres to pull t back, untill you can pull it back into the server room.

Note, if for some reason you have to retrieve something like some specially built cat 5 cable with a little plug on the end, try to tape that catch lever down to the plug will jst slide over stuff. If you leave leavers or screw in sticking out, you can bet your bottom dollar they will catch.

20 ethernet cords running out of the server?