When I draw something on the canvas, let's say a letter "L", then I want to make the drawing(The letter L) bigger, I try to Increase the image size. But when I do that, it deletes my drawing instead of making it bigger. How do I make an already drawn image bigger/smaller?

It would also be nice if I could Resize a selection. Thus making me able to resize only part of the image. I want to be able to stretch/shrink an image selection.
But anyway, how do I make a 1pixel wide letter "L" 2 pixels wide, without redrawing the letter "L"? (The letter "L" is just an example.)