Ad Rotation Plugin

I have a wordpress theme with predetermined ad spots. Within the theme’s each ad spot has a window in which I can place banner code. Doing so displays that banner, in that spot, on every page that has that spot, for every viewer.

I’d like to be able to have rotating ads so that

1) I can have more ads than I have ad spots (ie: I have 15+ 300X250 ads, but only 6 spots for banners of this size; 3 at the bottom of the home page and 3 on the side of any given page.)

And 2) So that the same ad doesn’t show in the same spot, every single time a page is loaded.

I know there are ad rotating plugins, but I’m not sure how to interface the plugins with a theme that already has determined ad spots.

I’m not very coding savvy, but I can follow directions well. If anybody knows how to accomplish this, or knows of a how-to guide or video on the topic I’d much appreciate it.

If you need specific information like screenshots or html code, let me know.

Thanks in advance!