I've always wanted something a bit more polished for a boot manager and found Burg (Brand-new Universal loadeR from GRUB)
Here's how I installed it.
sudo add-apt-repository ppa:n-muench/burg sudo apt-get update sudo apt-get install burg burg-themes sudo burg-install /dev/sda (please check the name of your drive) sudo update-burg
F2 allows you to choose what theme and F3 will change the resolution.
please bear in mind adding a repo can be a security risk, I don't own that repo nor have the ability to check how genuine it is, us at your own risk.
Using sudo with boot managers can brick your machine, have a live distro handy in case you make a mistake!