ive bought some new barrels to fit into my td5 with the push button handles, problem is i can't see how to get the old barrels out, so any advice is welcome

buster has done a write up fella, have a search on his section.

I just recently did this on my 300tdi 1997 push button. I guess yours is the same.
use busters demo to remove door card http://www.landyzone.co.uk/lz/f41/front-door-removal-75931.html

Except if your window wind doesnt have a central screw, then pass a piece of cloth (duster etc) over the handle and use a sawing action to pull of a 'U' shaped clip.

on mine I didnt need to follow busters door lock removal because mine was slightly different and I didnt need to remove the large metal internal plate nor support the glass mechanism.

I found by placing the key in the lock and holding it sideways I could undo the philips screw on the back of the plastic lever attached to the lock barrel with the screwdriver at an angle.

The barrel came out with an extension piece which by holding down a small pin can be pulled off.

You dont have to remove the outer door handle

Have fun