Depending on what equipment you have available to you there are a few ways to remove them.
Use a lathe as Trev suggested which is what I do.
If you dont have a lathe you can use a threading tap, find one that screws into the bush and then knock or press it out.
If you dont have any of that stuff a hacksaw blade held in the hand will work. Just carefully slot them until they come loose. The gear is hardened so at worst you will only scratch the gear if you go too deep.
After you have fitted the new bushes, making sure you have lined up the oil holes in the inner bush, you may have to ream them to size. If they do need reaming then once again if you dont have a reamer then you will have to take them to a engineering place. Reaming the bushes is a simple job so they shouldnt charge much to do it.