It seems like the headset bearings on my 2009 Cervelo S1 might need replacing. The headset has a reproducible click/creak when there is pressure and upon minor handlebar turns

This is my commuter bike and I've been doing most maintenance myself for a year now. I have never replaced threadless headset bearings before and wanted to make sure I bought all the correct parts before I start taking the bike apart.

The bike has a 3T Funda pro carbon fork (1 1/8" steerer) and a Cane Creek ISLT headset.
What size headset bearings do I need to buy for the replacement ? Since this is supposed to be an Integrated headset, do I need a headset press to install the new bearings or would I just be able to press in by hand ? I imagine I would need to get the headset bearing removal tool.

Thanks, V