You will need to install a custom recovery. You can do this with/without root depending on availability of PC(with pc you can do without root). Most roms come pre-rooted. So, it doesn't matter if you don't root also. Remember that after installing a custom rom, you can't use banking apps. It's better to do this if you have another phone as your primary device. For installing a custom rom just follow a youtube tutorial, they are easy.