All you need to do is installing burg and using it instead of grub , for installing press Ctrl+Alt+t for terminal and copy paste or write the following commands..

for adding ppa:

$ sudo add-apt-repository ppa:n-muench/burg

Update repository:

$ sudo apt-get update 

Install Burg:

$ sudo apt-get install burg burg-themes

Update your bootlaoder:

$ sudo update-burg

Its Installed now , restart your computer and press F2 for changing theme and F3 for changng resolution

For Customization directly without rebooting second time :

go to synaptic and search for burg and install Grub Customizer if its not installed .It will ask you BURG found! Do you want to configure BURG instead of grub2? press yes.

Install it to MBR to put Burg down as the default (over grub).Accept the default value unless you are booting from a hard drive other than the first one. If you're unsure, leave it as it is.

Now open your terminal and write

$ sudo burg-emu

press F2 and change your theme,and for downloading and installing other themes google the terms , you will get what you want .