Not enough space on HD to update macbook pro
When I agree to the terms for updating the laptop, it says that there's not enough space on the Macintosh HD.
Mac Pro
There is no arguing with the installer. You will need to remove data from your Mac to the size the installer tells you is lacking - and a bit more. You can park it on an eternal drive and put it back on later.
Or see this as an opportunity to tidy up some content you don't really need on your computer.