How to extend my Post-graduate work permit, IMM 5553E or IMM 5580E

[yduck]

Hi, guys

I have been working for 7 months in Canada under a post-graduate work permit after I obtained my 2-year graduate degree. My current Post-graduate work permit will expire in Dec. 2009, because my passport will expire then. Now I have got a new passport and I want to extend my post-graduate work permit until 2011, which I am eligible for. But I am confused about which Instructions I need to follow.

IMM 5553E (Applying to Change Conditions or Extend Your Stay in Canada -Worker) or
IMM 5580E (Applying for a Work Permit - Student Guide)

When I first applied for the post-graduate work permit, I followed IMM 5580E. But I am not sure if I should still use this one for extending the permit, as IMM 5553E seems to be more suitable to my current situation. Please help.

Thanks a lot