DIY a size 10 into a size 14?

I'm a little new to the DIY thing and I've seen really cool tops in shops that I'd love to wear, but only go up to like, a 8 or 10. I was wondering if there's any way you could convert a smaller size top into something a bit more roomy? How would I go about slogan tops, as all I really want is the slogan/picture on front? Step by step would be great :)