Many IDE's provide a function to find and replace across files in your project, of course VIM can do this too by using the "arg" commands, without switching to the terminal!
There are 2 steps to the task, first we provide a set of files for the replacement to happen on. The second part is telling VIM what to replace. Take a look at this example:
Of course this is a contrived example, you will likely want to specify which files are used and you may not want to replace every instance of your search, so additional options can be added.
Notice that you can use the unix "glob" pattern to specify the file locations. Additionally, adding the "c" flag to your regex will inform VIM to ask for a yes/no response on every match before replacing.
For help learning regex, take a look at the following sites: