If you want to uninstall oh-my-zsh, just run
uninstall_oh_my_zsh
from the command-line. It will remove itself and revert your previous bash or zsh configuration.
sh -c "$(curl -fsSL https://raw.githubusercontent.com/robbyrussell/oh-my-zsh/master/tools/install.sh)"
git clone https://github.com/bhilburn/powerlevel9k.git ~/.oh-my-zsh/custom/themes/powerlevel9k
Clone this repository into $ZSH_CUSTOM/plugins (by default ~/.oh-my-zsh/custom/plugins)
git clone https://github.com/zsh-users/zsh-autosuggestions $ZSH_CUSTOM/plugins/zsh-autosuggestions