Cut away as much paraffin as possible, place on warm plate to melt paraffin then place in xylene for 2 hours and then repeat xylene bath 2X with 1 hour incubations. Then 2X 100% alcohol, 2X95%, 2X 80% and then 1X50% all for 1 hour. Then place in water. This is based on normal sized tissue pieces, if you are doing large tissues then the times must be increased.
Why do you want to do this? If it is because the original fixation wasn't good then this won't help. We only do this if there were issues in the processing (example someone mixed up the xylene and alcohol solutions on the processor).