Changed URL cannot Log in, need walkthrough

I accidentally changed the word press address and site address URL and have no idea how to change it back due to the fact that I cannot log in.

I am a new user of word press and I have searched the forums for the same problem and have discovered that my problem is not new.

I am however not very computer savy and do not have word press installed on my computer. Can someone please give me a step by step walk-through because I have no idea what I am doing.

Someone please help!