How do I uninstall Ubuntu 16.04 LTS in a triple booted (with Windows 10 and Kali Linux 2) and reinstall it?

I have recently installed Ubuntu 16.04 alongside Windows 10 and Kali Linux 2. I have messed up a bit of Ubuntu by unpacking a lot of .deb files and now having problems with unmet dependencies, and I need to add more disk space to Ubuntu file system. How do I uninstall it safely, and reinstall it back after adding more free space for Ubuntu? The Grub of Ubuntu has overwritten Kali's Grub. I assume, formatting the Ubuntu partition will wipe out Ubuntu but not the Grub which will probably have Ubuntu's entry too.

How do I do it safely without messing things up even more?

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