You don't have to move anything as the ability to run WP as if its in the root folder when the files are in a subfolder is already built into WP. See this article
When you read the article, remember it was written for someone who had installed WordPress in the root folder and now wants to move it into a subdirectory. Your situation will be the reverse, but the solution is the same.
Just ignore steps one and six, and do the rest of them
Make sure you back up your database before doing any of the steps.
You should be all set.