If you are using form library and you have a defuault form template associated with it but you now have an update or new version of the form template. There is no need to worry about. Both the templates can work but the solution is a little different.
- Go To form library
- Click on Explorer View
- Copy the new / updated template with new name.
- Go to form libray settings
- Go to General Settings
- Rename the Template to new template.
- Old one will get opened or you can create new from them using Save As and work with new ones simple.