I have changed the boot priority to cd drive and tried and it appears that I am running from that cd with no offer to replace existing mint os.
If you indeed booted up on the DVD, then you will see an icon on the desktop to "Install Linux Mint." I'm pretty sure this is the only way you can install or reinstall Mint... by booting in "live mode" first. If you don't see this icon, then you are probably still booting into the Mint you already have installed. When you change the boot priority in BIOS, you have to "save changes".... or else you didn't change anything. You don't have to change the boot priority though, you should also be able to boot from the DVD when starting the computer and then hitting Escape or some F-key (like F10 or F12) before GRUB starts.
When you boot the DVD and launch the installer, you can replace the existing Mint, as
@arochester suggests, but you will have to choose the "Something else" option in the partitioning part of the installation so that you can pick the same partition that Mint is currently installed into. If you choose "Install alongside" the other operating systems, then you will have 2 copies of Mint instead of replacing it. If you want to get rid of Windows and have Mint only, then you can choose "Use entire disk" during the partitioning, and it will erase both Windows 10 and your first Mint install. Erasing Windows and using the entire disk is the easiest method, but you did not say that is what you want to do.
You must use care at the partitioning part of the install. The partition "layout" and how to use it is not always clear to new users. There are many sites that describe the install process and include pictures (
like this one) but your situation is a little different in that you will install into an existing Linux partition instead of installing into "free space." Those instructions also mention creating SWAP space (which you already have, so no need to do it again or create more). And those instructions also describe creating a separate Root and Home partition, but I would advise against that for new users.... just use the single large
ext4 partition that Mint already created for you, and be sure to designate it as
"/" (root).
Cheers