Deleting one linux operating system from dual boot linux setup

I have both Zorin OS and Ubuntu OS set to dual boot on my PC.  However, I would like to keep Zorin and delete Ubuntu but how do I do that?  Can it be done without affecting the Zorin OS or do I have to re-install Zorin and choose to wipe the whole disk and only re-install Zorin?  Please advise.  

I see you have been helped

https://forum.zorin.com/t/replace-ubuntu-with-zorin-without-affecting-user-data/7046/4

To remove a Linux OS from your computer, follow these steps:

1. Boot into the Linux distribution you want to keep.

2. Use a partition manager like GParted to delete the partitions associated with the Linux OS you wish to remove.

3. Update the bootloader configuration, typically GRUB, to remove the entry for the deleted Linux OS.