How to change default skin on a wiki?

I've been having difficulty changing the skin on a wiki I've created. I don't want to edit the preferences for myself, I want to change the skin for everyone who's coming to the wiki.How to change default skin on a wiki?
from this link , it does sound like you wil have to eit your preferences , ie go back , then save. Could you possibly copy your content onto say a blank background in paint or somesuch , then go back change your skin and import?. Im being honest to say ive never done this but ,in order to not lose content , i have copied stuff to notepad /or similar then pasted it back , rather than lose and have to retype.