Descripción de Fruitwise guide to grafting over an apple tree:

Grafting is easy, it can enable you to change the variety of fruit a tree bears. This technique, also known as top working enables you to replace a tree with fruit you don't like with a preferable fruit. Since posting this I have put up videos showing several techniques of grafting -saddle graft, rind graft and cleft graft. You are now (mid April) too late to graft trees for 2007/2008, but you can practice on spare wood and think and research about what if any grafting you would like to do next season. PS one useful aplpication of grafting is pollination. If you have a tree which is infertile due to lack of a pollination partner, you can graft a few bits of wood from a compatible pollen partner in to it. This is a video of an apple tree which was successfully top worked over to a better variety a year ago to show the usefulness of the technique.