How can I change the "short name" of my account?

I want to change the short name of my account because when my dad bought this computer for me he set up the account with his name as the short name and it has been bothering me ever since.

When I go to system preferences and then accounts my account is listed and when I click on it under password I am able to change my name, but not my short name because it is greyed out and cannot be clicked. Is there any way to change the short name on my account? I can't even delete my account and make a new one because the account delete button is greyed out when I click on my account.

Also, I went to my home folder and changed that from my dad's name to my name. This has reset every program on my computer to default settings! For example when I open my Safari browser a message pops up saying a keychain cannot be found to store Safari and asks me if I want to restore default settings.

So pretty much I've tried to change the short name on my administrative account, I reset everything to default settings and my short name is still my father's name. Can anyone help me out here?