Changed the WordPress Address URL [HELP!]

So basically as the title said, i messed up and changed my website URL from what i originally had it to something new, now i can’t load the website to change it back. Any ideas?

Old Address – http://www.sightdesign.net.au/

New Address – http://www.surrogate.net.au/

Really need some help on this, some-what worried. Is there anything i can do to fix this or have i completely f**ked up my website because of it.