using omnidisksweeper

Make a good backup before you do anything.

Is this as reported by Omni DIskSweeper, not the storage tab on your Mac? If that's what ODW is reporting, you need to be very careful not to delete any files from ~/Library that are important to your system. If you do not recognize them, then don't delete them.

Here is a list of all top level folders in your ~/Library, so you know what is default for Mac OS:

EDIT: Actually I see you are running Yosemite and I gave you default folders for Sierra, so your milage may vary.

Your email is in the home folder library

Your iPhone/iPad/iPod Touch backups are in home folder library

Your best bet is to post which library (as mentioned by Eric Root), the name of the folders and how much space is being taking up by the folder for the forum to give its advice.

Delete the wrong thing, and you will become a doorstop 🙂

macjack wrote:

BobHarris wrote:

Delete the wrong thing, and you will become a doorstop 🙂

I certainly hope the OP will not turn into a doorstop.

I for distracted. Someone in "Meat Space" wanted my attention, while I trying to finish writing this.

That is my excuse, and I'm sticking with it 😀

Which Library? Hard drive level Library, System/Library, or your user Library? You don't want to delete anything from the System/Library.

BobHarris wrote:

Delete the wrong thing, and you will become a doorstop 🙂

I certainly hope the OP will not turn into a doorstop.