Recipe calls for shortening, I want to substitute butter. Do I need to melt the butter?
No, shortening is a solid fat. This means you have to substitute another solid fat, else the recipe won't work. So, use the butter as it is. 

You probably will have to bring the butter to room temperature to be workable (shortening hardens less in the fridge). Don't use the microwave, it will produce melted spots. Leave it out overnight or longer, or, in the worst case, shave it into small sheets and leave these out for an hour or so. 

Your texture will differ somewhat from the original. Lard might be the better substitute for shortening.