New HDD, 2nd windows install. Need help

I stuck a new HDD into PC and is currently set as 2nd HDD.
It is blank and new.
What I want to do is install windows 10 on this drive , and set it to the main boot.
The problem I am having is what is my best option.
Do I do a windows 7 install on new HDD from DVD? or Flash Drive?
Is there something I can load onto the new HDD that will start installing windows 10 on it?
If I do traditional DVD install do I leave key empty and start installing updates ?

The main reason I am doing a HDD change is because the old HDD is starting to fail.
Will still put the old HDD as second boot, so can still get the data off of it.
What data should I make sure I copy? Was thinking USER folder.

Seconded. Definitely do the verify, last thing you need is if the 1st drive glitches during the procedure.

If you want to do a clean install to the new hard drive, then you will want to disconnect the old hard, connect the new hard on its place as the first hard drive, and leave the old one disconnected.

Boot the computer from a Windows 10 USB flash drive or DVD. Skip entering a product key, if asked. Install the same Home or Pro you had before. Select the custom install option, delete any existing partitions in the list (new hard drive should not have any). Click next to install to the unallocated space.

Windows 10 should activate itself. Then reconnect your old hard drive as the second hard drive. If you don't do it that way you will probably get the boot files for new Windows 10 installed into the old hard drive and end up with a mess.

Ok what I did is load windows 10 exe on a flash drive. Then told my friend ( the one updating PC) to shut PC down, unplug the old HDD, then boot from USB.
It should work flash is bootable.
Then told him to install windows as normal.
Once done reconnect old HDD. and start installing software on new HDD, and any settings, bookmarks etc. move from old to new.
This should work, but probably wont be until next week when he gets it done

Well tried today.
Ended up trying from a USB drive. But did not want to boot in the bios for some reason. USB was seen fine, just didnt boot.
I then tried to do install using DVD, but the drive was an old IDE, so used an adapter to hook to USB.
That failed as well. It kept kicking back to second boot selection.
Went to WinToHDD, installed software and started process of cloning.
All was going well, it rebooted to new HDD and then failed as it hit 100%. Took a few hours to do it this way.
Had to download the ISO from windows site.
And tried WinToHDD again with loading from the ISO onto the new HDD.
That finally worked.
Now just to get programs situated on the new HDD and move some files over and it should be golden.

Thank you for all the help and suggestions, it really helped.