If you are an active subscriber (meaning you purchased a Nios I/II kit less than a year ago or you purchased a Nios renewal and are still under active maintenance) then you will receive updates shipped to you automatically. We generally have 2 shipped releases per year, and 2-3 downloadable service pack releases.
Check for downloads here: nios i/ii service pack downloads (
https://www.altera.com/support/software/download/service_packs/nios/upd-nios_index.jsp). Warning, please do not mistake Nios I service packs for Nios II ones. The next release is a service pack, scheduled to be available for download from
www.altera.com by October 15th.