It depends on what files. The simplest way is to just install a file explorer app if it doesn't have one (e.g. ES File Explorer), find the files you want, select files (or long-press on the file) and then delete them.
If you mean pre-installed system apps then you'll need to root the phone before you can remove them (though on Android 4 or later you should be able to disable the apps, which will be as good since you don't gain space by removing system apps).