Change band into different type

38mm and 40mm watch faces use the same band

42mm and 44mm use the same band

What Size Watch Band Does My Watch Band Take

In the Watch app on your iPhone go to My Watch, then at the top of the page tap All Watches. You will see the entry for your watch, including the case size. This tells you which band size you need to order, for 38/40mm or 40/44 mm case.

If you purchased through the Apple Studio program you can exchange it for another band, if the one you want to switch to is more expensive you will have to pay the difference. If you did not you won't be able to exchange it.