my start up disk is full

Hey there eddibuck1,

I understand that you need more free space on your startup disk. Here is some information that will help you address this issue:

Freeing up disk space

If you need to increase the amount of available disk space on your startup drive, examine the items in your home folder. Look in the Documents, Downloads or Desktop folders to see if there are any files you don't need anymore. Use these suggestions to reclaim disk space from these folders:

• Delete items you don't need, or have copies of elsewhere, by dragging them to the Trash.
  Once you're sure you don't need the items in the Trash, empty the trash to reclaim disk space. From the Finder, choose Finder > Empty Trash.
• Move items to another drive, such as an external hard disk or flash drive.
• Compress items you don't use frequently. Delete the originals of these files and keep the compressed copy instead.

Be sure to only delete items you no longer need, or have copies of elsewhere. It's a good idea to create backups of important files in case you accidentally delete an important item later.

See this article for additional suggestions on how to increase disk space.

OS X: What is "other" space in About This Mac? - Apple Support

https://support.apple.com/en-us/HT202867

Take care, and thanks for visiting the Apple Support Communities.