I'm assuming here that you have standard laminate tops and not a synthetic (Corian, etc.) or post formed tops. Start with the back splash. There may be fasteners hidden beneath the toe of the splash. Then check for corner cleats with screws up from below or screws through the upper frame stretchers into the substrate. If not then the top is probably screwed or nailed from above and laminate applied in place. If that's the case, get the pry bar & pop off the laminate, then cut up the substrate & back out the screws or pry it up if it's nailed.