First Method:
I created 2 registry keys one to enable this function (open new excel instance every time) and one to revert to how it was.
New Instance Every time Registry Key
Revert to Default Registry Key
If it does not download by clicking on the link....
Right Click and Select "Save Link As" name it, and leave it as (Registration Entries)
Once downloaded just double click on it and click yes.
PLEASE NOTE ANY FILE THAT MAKE CHANGES TO YOUR REGISTRY WILL GIVE YOU A WARNING AT THE MOMENT OF DOWNLOAD.
THIS IS****NOT MALICIOUS . I'm just trying to help!!
Second Method:
Another Easy way is to add a shortcut to excel in this location. (enable show hide files & Folders in windows)
C:\Users%username%\AppData\Roaming\Microsoft\Windows\SendTo
-now the only thing you would have to do is right click on the excel document you want to open.
-go to "Send to"
-Select Excel
-Now it will open on a new instance of excel.
Hope it helps!!