Changing cheek pads to change the helmet fit:
All sizes of cheek pads are interchangeable in all helmet sizes
These cheekpads are sold in sizes corresponding with the original helmet size they are in. If you just need a refresh, then order the size that matches your helmet.
If you need more room then you will want to order the cheekpads that fit into a larger size helmet, if you need to tighten the fit then you need the cheekpads for a smaller size helmet. This might seem counter-intuative but a smaller head needs more padding to fill the space and a larger head needs less padding.
Cheekpads typically vary about 5mm between sizes so if you think you need more space than that then you might want to get the pads that fit the helmet that is 2 sizes in the desired direction.