Changed directory by mistake

I was tinkering with my site and have screwed it up.
https://www.wildmedic.co.uk

I was trying to put a splash page on, which I did successfully. Then I tried to change the link from my logo from https://www.wildmedic.co.uk to /homepage. I changed the wrong setting in the settings menu where it asks which directory you want it to be changed into (ie the second one down). Now when I go to the site it says internal error 500. How can I change it back! Help!