How to use Antigen if oh-my-zsh was installed previously?

[Myron472]

Zsh has some default parameters in .zshrc configuration file. However, when installing oh-my-zsh it changes .zshrc file completely by removing all previous strings and inserting it's own ones. That is the thing I'm not sure about when it comes to installing Antigen.
I have searched on the internet how to install Antigen if I have installed oh-my-zsh before but I didn't find anything related to this topic.
So how do I install and setup Antigen if I have installed oh-my-zsh previously? Do I just have to delete everything in .zshrc file so it will become an empty config and just add Antigen commands there? Or I have to completely remove oh-my-zsh and then install Antigen?

Also It would be great if Readme would have a paragraph dedicated to explaining how to install and use Antigen with oh-my-zsh installed previously.