Changing aperture on Canon SD500?

I just got the Canon Powershot SD500, and I've read that it has several manual control options, including aperture... But I can't for the life of me figure out how to change the settings for aperture? Are we manually able to change them ourselves? All I really want to acheive is a shallow DOF so the background will be blurred like in this post. I tried zooming in all the way like the post suggested, but that didn't help. I wasn't able to get a whole lot of room between the subject and background like the post also suggested, but it should have been enough.... Any suggestions?

Anyway, thanks so much for your help :)
Amanda :)

I have an S230 (an older version of the SD500 and it only has "infinity" and "macro" modes. To the best of my knowledge the ELPH line does not offer any real control over aperture (it has a "manual" mode, but that's a total misnomer). You can sort of do a blurred background, but you have to have the subject pretty close to the lens to do it. Here's a couple I've been able to get with my S230....

Thank you. :) I tried a few test shots yesterday where I was able to get a lot of space between the object and the background, and the background was a little blurred, but not extremely. I like REALLY blurred backgrounds. :) Oh well. :)

Thanks again for your help :)