It's very convenient to change the Apple Watch band, which is also one of the prominent features of Apple Watch design. Prepare the Apple watch and the new band. Follow the steps below.
1. Flip over the apple watch. On the back of the Apple Watch, you'll notice a release button at each end close to where the band joins the watch(as shown in the below figure).
2. Gently press your finger on the band release button, then slowly slide the connecting rod of the band outwards along the watch edge. You'll remove one side band.
3. Repeat it at the other side to remove the band totally from the apple watch.
4. It is also very convenient to replace the strap. Hold the new band and start from where the old one fell off just now. Simply slide the connecting rod of the band from one side into the band groove until you hear a slight "click", the band is in place one end
5. Do it again at the other end. The apple watch band is done changing.
(1) Attention should be given when assembling the new band to the band sides. Don't reverse the band front with its backside. Otherwise, you'll have to take the trouble of reworking the process.
(2) Besides, bands of 42mm and 38mm are not interchangeable, so replace it with one of the same size.