Of course you can wait a few hours till dawn in Australia and
@wizardfromoz appear inside a puff of smoke
(Wizard appears in a puff of smoke, yawns, scratches where the sun don't shine, goes for 3rd coffee)
Morning all from DownUnder, and welcome to linux.org
@Kevin George
Kevin, do I take it you have a working copy of Mint at the moment?
You could tell us which one it is with the full name of the .iso, for example
linuxmint-18.3-mate-64bit.iso
or
linuxmint-19-xfce-64bit-v2.iso
... etcetera
If you got the .iso from Linux Mint's official site linuxmint.com chances are the iso is good, but it is best to check these things, if only to eliminate a defective or incomplete download if things go wrong.
If your Mint is up and running, and it is of the 18.3 'Sylvia' Series, or the 19 'Tara' series, then a product called Timeshift is already installed.
I would be inclined to take a snapshot of your existing setup with Timeshift, and then download GParted Live from here
https://gparted.org/livecd.php - you can put it on as small as a CD or a 2GB USB stick if that is all you have. You could then boot from it and resize your drive to the full space available.
Alternative is first to establish that the .iso is OK, and then do a clean install, allocating Linux the entire drive.
When you first installed, you would likely have had a screen that looked something like this
... and it is
there that you may have gone wrong and lost your Windows.
If you really want your Windows back, then GParted Live also has a facility for Data Recovery, but I have not used it for something as complex as Windows.
So think about these options, and when you have made up your mind, let us know and we can steer you.
WIZARD'S RECOMMENDED READING
For Hashsum Checking under Linux, of .isos
https://www.linux.org/threads/gtkhash-–-hashing-out-the-basics.4430/
https://www.linux.org/threads/hash-checking-rare-tips.13544/
For Timeshift
https://www.linux.org/threads/timeshift-similar-solutions-safeguard-recover-your-linux.15241/
or Linux Lite's Manual has
https://www.linuxliteos.com/manual/tutorials.html
... and click on Timeshift
Cheers
Chris Turner
wizardfromoz