I am not able to make my world creative or not be a member.

I'm new to Minecraft and i just started 2 days ago. I was able to switch my world to creative and i did that. But now i can't and i want to! Also i don't want other people coming into my world so i didn't want to be a member, but now it won't let me change it I don't have Xbox Live or a Xbox account. Please help me!

P.S for the 'affects versions' bit i didn't really know what to put so i put 1.2.2.3 because that was the closest one to my version(1.2.2)