If you have a better method then there is absolutely nothing wrong with posting an answer and accepting that instead, just as there would be nothing wrong with changing the accepted answer if you had a new and better answer from someone else. The accepted answer should be whichever answer you believe to be most useful; if that changes, change the mark.
As DᴀʀᴛʜVᴀᴅᴇʀ said, the +250 is from a bounty and won't be affected by changing the accepted answer. Changing the accepted answer will take away the +15 originally awarded for accepting the answer. 15 rep is not a lot though and that shouldn't really affect your decision in which answer to accept and whether to change the accepted answer or not.
If you are going to change the accepted answer to a self answer then make sure your answer is actually adding something new though; if your answer is just restating or consolidating what has been said in other answers then I would consider posting an answer but leaving the accepted mark on whichever answer helped you the most.