i was able copy the hardrive of my old macbook from "My Passport" onto the desktop on an older iMac. but i dont know how to make my hardrive and user name be the main one since someone had used it in the past and had their info on the comp. please help!

I recently broke my 2008 macbook. i was able to use an external hardrive to back up my data onto My Passport. I was going to buy a new computer but a friend told me sher had an older version of the iMac. (not sure how old but it doesnt have a camera if that helps) i was able to hook it up and turn it on but i ran into a few problems. 1) the "authentic" user or whatever it says is someone who previously used the computer. i added me as a user but im not sure how to make me the main user. 2) after hooking up My Passport, i was able to drag my files and copy them to the desktop.(i think i did it correctly) now, i dont know how to make my hard drive and applications and iformation the "main " info. The current apps on the iMac are super old versions of iTunes and iPhoto and such. 3) while trying to open the apps from my macbook on the iMac, it said it didnt have the right software to open these apps.

I am so computer illiterate so someone please help!!! Also, i do not have internet in my new apartment yet so if there is a way to make this happen without using the internet that would be preferred. sorry for the horrible spelling and poorly written paragraph. 🙂

THANK YOU!!