Need to add extension to Make 2017

I am trying to add add an extension to export skp files to dxf for cam software but cannot find a way that works. I have tried to add an account in Extension Warehouse but it just times out. Can anyone help please?

Why ?

See the Guide:

Thank you for your replies gents. Since I posted I have successfully installed skp_to_dxf.rbz using Extension Manager and I can now export dxf files. Thanks again.