How much free space is needed for this update?

[wrm1]

Can anyone tell me how much space is actually needed for this update? I downloaded the update to my sd card. It said I needed 5 GB to install so, I cleared apps and such so that I have 6.17 GB free. Now it's saying I need 8 GBs free to install. What are the actual needs for this update and is there an iso just for the update or is that the full install again.?