Go slow! If you make a fast switch your pet may have diarrhea and belly aches. Maybe even some puking. The process of digesting kibble and raw meat is totally different, hence the much needed slow transition.
You can start with 3/4 what they are eating now and 1/4 raw. If you want to go slower, you can start with the raw meat as a treat and build from there.
If your pet does end up with a belly ache, you can pick up some digestive enzymes and maybe some probiotics to add to their bowl.