Pitting stone fruit can be tricky. First, cut along the seam of the fruit all the way around, using a serrated knife. Then, gently twist the two halves and pull apart. You should be able to pull the pit out from the fruit half. If not, lay the half with the pit on the cutting board, pit side down and with your paring knife, carefully cut wedges of fruit around the pit.
If the fruit is too ripe to twist the two halves apart, similarly, you can use your paring knife to cut wedges of fruit from around the pit.