If you have already created a template, but would like to add a new column or delete an old one for further import, you do not have to create a new template.
Simply edit your existing template:
And this is how it works:
Go to the "Import/Export" menu
Click on the "objects tab" and then on "File Format"
Click on the edit icon of the template that you want to edit
Edit the template the way you need it
Tip:
If you need more help, check out the article on creating a template here.