How do I change spanish to english on a pc?

I know that other people said to just go to regional control from the control panel and u can change it from there,but the person that had this pc before us(it's used)said he deleted english from the pc... So when I tried to change the default language to english which I umed in Spanish was Ingles(Estados Unidos)?I did that but nothing happened... I also heard that u might need a windows xp cd so u can install that into it or whatever... So could anyone tell me how to get in back in english?And I'm not too tech savvy,I've never dealt with anything like this before so could someone please tell me in a way that I'll understand?Thx.