It's best (although not required) to install pathogen, which allows vim scripts to be bundled and installed separately:
mkdir -p ~/.vim/autoload ~/.vim/bundle
curl 'www.vim.org/scripts/download_script.php?src_id=16224' > ~/.vim/autoload/pathogen.vim
And initialise it in your .vimrc:
echo 'call pathogen#infect()' >> ~/.vimrc
git clone https://github.com/featurist/vim-pogoscript.git ~/.vim/bundle/vim-pogoscript
To update:
cd ~/.vim/bundle/vim-pogoscript
git pull