Need simple help with i tunes (i hope it's simple)?

My sister just got an i-pod for christmas, and i also got a psp. My psp will not tke WMA files so im using itunes to convert my songs. but at first, the songs on itunes was in a weird format that my psp would not recognize, but now i converted them all to AAC files ,which i know my psp will recognize. but another problem have came up, now i have duplicates. my itunes library is now full of duplicates and In some cases, triplets of songs that i am dieing to get rid of. Is there any way to do that without doing it one by one, like maybe to group them. I tried to just filtering out all of the AAC files but even they got duplicated for some reason. If i check a Group of song and then delete them, can i do that. i've been trying, its not working that way. is there anyway i can do that without cleaning out my whole itunes and starting over or deleting them one by one?