Easy. There are many online audio editors. I'll make the list for you:
It’s free and can edit audio tracks fast. And you can choose the needed function on the menu bar, like the audio cutter, audio joiner, audio converter, etc.
It can cut MP3 files on the fly and will convert MP3 files. Also, it is a tempo changer and audio reverser.
A splendid online MP3 cutter and joiner.
This one operates like Audacity in some degree and can cut off the unwanted portions, normalize audio, add fade in/out effect, or zoom in and out on the wave form.
It renders a friendly interface and you can easily find the needed functions on the official page, like cut, combine, add fade in/out effect, and mute or adjust volume.
Source from: http://www.videoconverterfactory.com/tips/top-5-online-mp3-editor.html