For the past couple of days, I've been getting the message that I'm unable to save/download something because the startup disk is full. It says I have about 81 MB left (I believe that's the number, last time I checked) but the bar is completely filled with yellow.

You can see what version of the system you are using by going to the Apple menu, selecting About This Mac and clicking the Overview tab. If your Mac is running OS X El Capitan (version 10.11) or earlier, you need to to use the storage-optimization feature. If you cannot (or do not want to) update your Mac’s operating system, you can by deleting unneeded files, old mail attachments and other clutter. You can also find programs to automatically sweep your computer and collect unnecessary files. ($40, with a free trial period available), (on sale for $19, also with a free trial period) and the free are three possibilities.

They're additional categories that I've made outside the calendar which is tied to my account in Outlook, and they don't show when I'm in the window which lists categories on my account and allows me to add or delete. The problem is that the categories I'm trying to delete aren't listed under any account. I've been trying to delete some categories that aren't listed under my default account in Outlook 2016 for Mac, but it seems like it's not possible, which is baffling. How to delete a calendar from outlook for mac.

Insert the Windows installation disk in the drive and then exit the setup after saving the changes. Format for windows and mac. Once in the setup, ensure that the boot configuration is set to allow the CD/DVD drive to boot first.