How can I change the default language on my Windows 7 machine from German to English?

I bought my desktop from Best Buy. It's a floor model, so I got it on the cheap. When I got home to set it up, I found that the default language was German. I don't speak it, so I'd like to change it back to English. Help is much appreciated. I'd rather avoid reformatting the machine, but if that's necessary, someone might have to walk me through the process, since, again, I'm not fluent in German. Also, don't suggest I use Google Translate. I've tried, and it's more difficult than it seems. Thank you!