Use a small drill bit and drill a series of holes through the rubber, it will eventually grab and come out in a few pieces.
You need the sleeves for the replacement bushings unless you bought new ones. Clean the sleeves out good, most new bushing come with some type of liquid/silicone to put on the new bushings before pressing them back in the housing. They are tight to get back in, you can make a press to do it or press them in by hand and use a deadblow hammer or a hammer and a block of wood.
Maximum Motorsports sells a nifty little tool to install and remove them as well.