How to unmount a partition before reinstallation?

To have a fresh installation I was told I need to format the partition it is on and simply re-install Ubuntu. I am currently on a live cd and was going to format it but apparently its mounted so I can't format it.

I'm not sure what to do and I would like Ubuntu back with out screwing something up. Btw I dual-booted it so I would also like to do this without screwing up the Windows partition.

screenshot of gparted: Lspci:

to unmount your partition

• open gparted
• right click the partition you want to unmount
• select the unmount option

You should not need to do any formatting ahead of time. If your dual boot configuration is working properly, you should be able to boot the system from your installation media (CD or USB device).

Backup any data you may want, if you can, before proceeding. You could lose it otherwise.

You can choose either 'Try Ubuntu' or 'Install Ubuntu' which then would need you to click the Install icon from the desktop.

Once the basic install process begins, it should scan the system drives and ask you if you want to replace the identified operating systems, replace everything, etc.

Choose the option to replace the previous Ubuntu installation.

That should reinstall ubuntu clean over the previous instance without touching the Windows partition(s).