That's the question. I would like to delete some of my answers that have been accepted. How can I do that? Everytime I hit delete it is not possible for me to do so.
Try to get in touch with the OP (by posting comments to either your answer or the parent question), and request that he unaccept your answer. Give a good reason why the answer should not have been accepted.
If the OP unaccepts your answer, great! Problem Solved!
Flag for moderator attention, include an explanation of why you want the answer deleted. We generally only act in extraordinary cases (answers that are demonstrably wrong mathematically, answers to on-going contest questions, etc.) So try to be convincing. If there is a mathematical problem with your answer, you, or someone else, should have already commented to point out the problem (see Step 1), in which case it suffice to ask the moderators to check the comments to see why the answer is mathematically wrong.
Do not, in any case, try to blank out the answer yourself. The system is designed that way (not allowing you to delete an accepted answer) for a reason, and trying to circumvent that can be considered vandalism.
If it is a case where you do not mind the answer remaining, but just do not want to be publicly associated to that answer (you do not want it shown that said answer was given by your user account), you can try contacting the SE team and request that that particular answer be detached from your account. I cannot guarantee that they will do this for you, and you need, again, be convincing as to why. But it is theoretically a possibility.