upgrading cams

[ace305]

I have set of stage 2 custom cams from MMR. I purchased Trick Flow Spring kit. Kit contains springs, seals, shims, locks, retainers. The kit came with 16 shims. How do I know to use the shims or not?

thanks

https://lmr.com/item/TFS-2500500/96-04-Mustang-46l-2v-Trick-Flow-Valve-Springs-Upgrade-Kit