Ok Metal_Gear_Ray, i will try to explain you a bit how to change file extensions.
You have a zip file and you must rename it to a mp3 in order to listen the song. Well, firstly, open your "My PC". In the top you have different menus, like File, Edition... Click on the third one (It´s something in english like see or watch).
Now, in the bottom of this menu you have to click in FOLDER OPTION. It will open a new window with 3 labels. Choose the second one, again see or watch, I don´t know how it is called in english.
It will appear a lot of options about files and folders. In the 5th mark or about you have a option that says:
Hide extensions of well known files or something like this. This option must be clear, without a "X". Accept.
Now, if you go to My Documents or any file folder, you can notice, every file has the extension in its name. Don´t erase completly this extension cause archive won´t be recognized by Windows. But YES you can change the extension easily.
For example if you have Metallica.zip, erase the zip extension and write mp3. Now, if the file is a song, you will have a mp3 file.
If you follow these steps you´ll do it easily, if have problems, tell me.