From the Dynamics GP Support and Services Blog comes help with Updating the Year stamp on the W4 in HRMSSS/Business Portal
Updating the Year stamp on the W4 in HRMSSS/Business Portal – Dynamics GP Support and Services Blog – Site Home – MSDN Blogs
Archived post from 2011. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.