Always enjoy helping others while using my phone's screen shot capabilities..
Note: Although I'm using the LG Android Rebel, Your setting may be slightly different.
1) Select an .MP3 you want to use a your official wake up alarm via your computer.
2) Connect your smart device to your computer and located your devices within the file tree (should be listed as or signed a device name you've given it)
3) I've selected Sirens By Achoo (which has nothing to do with vehicle sirens)
4) Opening a separate window while the device is connected.. transfer the .MP3 to your "Alarm" folder as indicated by this image:
Image: To access this view from your smart device, Settings > File Manager
5) Once you have 2 windows open; One being the location of your .MP3 and the other being the smart device's alarm folder window.. click and drag the .MP3 to the alarm folder.
6) Check to make sure the .MP3 transfer was successful as indicated by this image:
7) Locate and tap the "clock" app
8) Turn the alarm on
9) Scroll down to the alarm settings as seen here:
Note: Two areas one needs to focus.. the Alarm sound & Alarm volume..
10) Tap the "Alarm Sound" and locate the .MP3 you've just transfered to your device as indicated by this image:
11) Select or highlight the .MP3 (image above) Once selected, the .MP3 associated with the alarm should sound as a verification to your selection.
12) Return to the previous screen and select the "Alarm Volume"
13) Using the slider bar.. slide the alarm volume to the desired setting.
Also, if this tutorial helped you, please give it the "thumbs up"
Thank you.