Tempdb - Add additional file shrink primary file size

Hi -I have a system where the primary tempdb datafile is set to 12 GB, but there are no additional data files. I need to add additional 7 data files to have at least 8 data files assigned to the tempdb each with initial size of 512 MB and 256 MB autogrowth. Per Microsoft recommendation it is advised to give the files the same size, now with the primary tempdb set to 12 GB, and rest to even sizes, how should I go about making primary same size? Am I supposed to shrink the file to 512 MB, please advise.Thank you.