Is there a simple way to upgrade cams on a zetec? If i went for the Kent race cams.....is it a simple swap or would i have to buy other bits to make them fit?

My cam cover is away for shot blasting and powder coating so may as well get a few more bhp while its off

pretty simple swap if you are ok with re-timing on installation.

a set of vernier pulleys as recommended and you will need a remap afterwards

What sort of gains would that achieve?

IIRC If your engine is a Blacktop you will need to adjust the valve clearances which use different thickness cam followers as shims so not as easy as just fitting and timing the cams. Silver tops use hydraulic cam followers so no adjustment needed. Fitting race cams may make the car difficult to drive in traffic , common mistake so think about what you use the car for

Also worth noting that depending on how wild the cam and how high you want to rev you may need hd valve springs and updated rod bolts, maybe pocketed pistons and a compression increase. Going too dramatic comes with costs and that’s without better breathing through intake, head fettling and a matched exhaust.

Depending on what you are running now and how big the jump don’t forget about the capability of your brakes and gearbox, plus your own ability to handle the extra power which is likely to be very peaky (in the wet?).