This article describes how you can define your own templates for document libraries. To do this, please proceed as follows:
1) Create a template of your choice via an Office app. The best way to do this is via "Save as" in Word. If you want to use an Excel template instead of Word, you must create the template via Excel.
2) Connect to your SharePoint with the SharePoint Designer.
3) Navigate within the SharePoint Designer to the library for which you want to define the template and open the "Forms" folder within this library.
4) Load the desired template into the "Forms" folder. The easiest way to do this is by drag & drop.
5) Now navigate in SharePoint (not the Designer!) to the document library for which you want to use the uploaded template and open the "Library settings" there.
6) Now please go to the advanced settings.
7) Here you must now enter the location or the name of the template and confirm by clicking on save.