To configure VIM to use spaces instead of tabs, you can either execute VIM commands or modify the configuration file.
If you just want to modify a single file, you can execute the following commands inside VIM.
:set tabstop=2 :set shiftwidth=2 :set expandtab
In order to change the global VIM settings you can edit ~/.vimrc file
set tabstop=2 shiftwidth=2 expandtab
Once tab settings are configured you can execute :retab at any time inside VIM to apply the new settings to the existing document.
More information is available on the VIM wiki site.