DT Swiss makes some of the best hubs on the market when it comes to price/performance and flexibility. You can't beat a Chris King hub, but when it comes to changing hub sizing and cassette free hubs, the design of the DT Swiss products is second to none. I took a 135mm QR hub with a SRAM XD cassette to a 142mm through axle with a Shimano free hub in literally only a few minutes.
To begin with, all of the adjustments to DT Swiss hubs can be done without tools, which is exceptional. The standardized parts (for them) mean that just about anyone can easily make this switch without too much trouble. I was given a wheel with a DT Swiss 350 hub but it was 135mm and QR, the bike needed a 142x12 through axle, and the transition was relatively straightforward. The DT Swiss 240 hub is more familiar to me, but the 350 acts in a similar way.
Below you can see the old caps (right) and the new caps (left). You only need an additional 7mm to change the wheel from 135 to 142. The good news is that you don't have to do anything to the derailleur or the brake rotor, they should remain the same with the new wheel inserted. They may need a minor tweak, but nothing that can't be done quickly and easily.
Start by taking the old caps off. You can do this by hand.
This is the end cap on the brake rotor side, simply grab the cap and pull it off. Depending on the amount of time that it has been on the wheel it may take a little more force, but ultimately it should just pop off.
Once off, you will be able to see into the hub, now is a good time to clean it out and re-lube.
You'll do the same on the other side, removing the cap and then the freehub. In this case, I am removing a SRAM XD cassette freehub. When you take off the freehub you will find a set of two star ratchets and a pair of springs. The combination is: Freehub body > spring > ratchet > ratchet > spring > hub shell. Again, having this side off is a good time to clean and lube the inner shell.
The normal DT Swiss star ratchets have an outer gear that engages with the freehub or the hub shell. There are inner "steps" that allow the two ratchets to engage when pedaling or spin freely when coasting. It is a worthwhile investment to go in for the 36-tooth or 54-tooth ratchet upgrades if you are running the older 18-tooth setup.
With the mechanism cleaned up and lubed, just slide the new freehub body on and presto! you now have a Shimano freehub.
Congratulations, you now have a 142mm through axle for considerably less than buying a new wheel.
