This is a pretty simple interface so I only see three options:
Leave it as is
Move the difficulty to a second screen that appears after the start button is clicked
Put the difficulty under the settings menu you have on the footer.
First of all I want to say I would rule #2 out because there is no need to make the user select their difficulty every play through. In the beginning the user may shift through a couple times to find the difficulty they like but then they will want to stay at that difficulty for a while (until they feel they have gotten better). So forcing the user to select the same difficulty every time they play is adding an unnecessary click.
Probably not #3
While I just made the case that the user won't often need to access the difficulty setting which would make you think the hidden setting menu would be best, they will still have to do it every now and then. Your current home screen is so simple that it has no negative repercussions for leaving the difficulty selector there. It is simple to choose if they need to but easy to ignore if they don't. Hiding it in the settings menu will at minimum add an extra click and at most the user won't know the option even exists.
So, #1 leave it as it
Unless you add more elements to the home page, in which case you might consider moving it into the settings menu.