The easy way is to install grub-customizer tool:

 sudo add-apt-repository ppa:danielrichter2007/grub-customizer
 sudo apt-get update
 sudo apt-get install grub-customizer

When Grub Customizer starts up, you’ll see a list of all the items that show up in the boot menu. To hide entries that you don’t want to see anymore, simply uncheck the checkbox next to them.

But also, you can do it manually, see [link](http://www.howtogeek.com/howto/17787/clean-up-the-new-ubuntu-grub2-boot-menu/).

For Fedora 20:

`sudo wget http://download.opensuse.org/repositories/home:/Kenzy:/packages/Fedora_20/home:Kenzy:packages.repo -O /etc/yum.repos.d/home:Kenzy:packages.repo
sudo yum update
sudo yum install grub-customizer`