It's pretty simple and managed by OSX. - Select a filetype you'd want to change the default application for and open the File Info (Cmd+I) - In the "Open with"

It's pretty simple and managed by OSX. - Select a filetype you'd want to change the default application for and open the File Info (Cmd+I) - In the "Open with" section, select the app you want to be the default app for the filetype - To persist the default app along the whole filetype, also click the "Change All" button right below it.