Ambassador Curt Hays shares some quick thoughts on choosing the correct wheel size:
Use/Wheel Size: Most commonly, the activity for which a pair of skates will be used seems to be the determining factor for a purchase. Keeping up with a group of your friends on the local trail usually does not require 90 mm wheels, and pursuing your cardio fitness goals may be better suited to skates with 84 mm wheels. For friends of mine who just want to skate with their kids, I point them at rec skates with wheel sizes of 76-80 mm. For those wanting to skate for fun and exercise in recreational environments or in urban environments for transportation purposes, I generally recommend skates with 84 mm wheels or a 84 mm Hi-Lo frame (which has 84 mm rear wheels and 80 mm wheels for the front two). If you need skates that enable you to keep up with your marathon-skating friends (as is my case), then you may actually need to get skates with wheels that are 90 mm or larger. The pros race on wheels that are 100, or even 110, mm in diameter, and many people who enjoy speed skating also opt for skates that use larger wheels.
You can find all the parts to replace the wheels on your K2 Skates here: K2 Skates Accessories
Along with making sure you have the correct wheel size, it’s important to also keep your bearings running smoothly. Here’s a youtube video on how to do so.