Edit: If below directions dont work, I found a short video on youtube: YouTube - How to crop music in Windows Movie Maker!
Do you have a mac or pc? I found these directions online if you have a pc, you can use window movies maker. I havent tried any of these, so let me know if they work.:
1. go to where u want to seperate it then click the "ctrl L"
OR
2. Use Windows Movie Maker. Open the program which can be found from the Start menu. Now add the song into your collection. Next, drag the file of the music into the music frame below. To shorten it, click on the ends of the bar (under the music frame) and drag it either to left or right to shorten the length of the music. Finally, save your file.
Hope this helps!