Getting the old bushes out... good luck with that
Big vice, hammer, failing that burn it out and use a hacksaw to cut the outer and chisel the remains out. If you're lucky it'll have poly already fitted...
I normally see if I can find a socket that just fits inside the hole in the radius arm and then put another socket on the other side that's bigger than the bush. That way you can either use a vice and the small socket should push the bush out... if you're lucky. Sometimes a hammer will work using the socket as a drift.
Getting the poly ones in...
Lots of lubrication !
If I can I normally use a suitable sized bolt, some big washers and a nut. Put a washer on the end of the bolt, put it through the bush then the arm, put the other big washer and nut on and start tightening. If you don't have a long enough bolt a bit of threaded bar will do the job just fine with a nut on each end. I use M10 bar normally.
The trick is to keep it as square as you can while using the bolt/threaded bar to apply the pressure. Once the lip has popped into the hole you're away and you can wind it all the way in. It doesn't take much pressure at all to get them in, in fact too much pressure can make it more difficult.
I've attached a pic that might make it clearer... the grey bit is the bolt/threaded bar, washers and nut(s).