I need help with this iMac i got from cleaning a church?

i got an iMac from a chruch and a program called ""Edubuntu" which is a program designed for little kids and this program undergoes 3 stages when i turn it on and i want to erase it and use this iMac for personal use. . . . .but this edubuntu program gets it my way. . .heres the full explanation. . . . . .when i turn it on it the chime goes off and the system undergoes 3 stages: first it goes through ubuntu bootstrap(which is basically where u choose where to use linux or CD drive) second : yaboot (version 1.3.13) and this is to load up all hardware and programs. . . . i guess***at that stage there is thing that says boot: and u type what but if u dont type anything it automatically goes through stage 3 which is the login page for edubuntu. . . . i dont have any software i dont know much about mac im using windows xp to post this question so please help me so that i can use this iMac for my personal use. . . . .thanks. . . .