how do i change the order of appearance for characters?

When you added them, did you also number them in the "Order" column? That column takes precedence over the order they are added in, so if no numbers are given there the list will simply be ordered alphabetically. To correct it you need to go to the movie page, use the Edit Page button at the bottom and choose Correct/Delete in the Cast selection at the top, then click Continue. You'll need to choose "Correct" in each of the boxes where it says "Keep", and then add the correct order numbers for each of them afterwards.

However, before you follow Cartman's advice, you need to understand that IMDb is not interested in "the order [you] want them in". The only order you should submit is the order in which they are listed on screen, even if this means the main characters do not appear at the top.

The Submission Guide: Order gives more detailed instructions.

Also, if you are planning to input the Order numbers for the full cast, you can check on the box beside Correct all at the top of the Cast update form instead of selecting Correct beside each credit. When you Check these updates, the system will change all the Keep:s to Corrects.