Make sure there are no other fixings holding the tops to the underneath cupboars. If there are then remove them. Tr to prise them off the cupboard tops with the use of a broad chisel and heavy mallet. This may have the effect of splitting the glue in the joint.
Alternatively, set your circular saw blade to a depth of about 1-2mm LESS than the worktop and cut along the joint. This will seriously weaken and glue holding them together, and then prise them up from below to separate them.