I have a new 38mm Apple watch but it does not fit. Are there bigger bands or can I switch the band out with a 42mm band?

The sizes of bands are set. The 42mm band will not fit on a 38mm watch. It has to do with the width of the watch. If your wrist is too large for a 38mm watch, then you should consider the 42mm. Each watch with band in the online store shows the wrist sizes the device is designed to fit. You receive two different bands when purchasing the watch, and if the longest band does not fit, you should consider the 42mm device. It is designed for larger wrists. Or, you can look to see if you can find a 3rd party band that fits your device that has a larger length.

Hi

All bands that can be purchased as separate accessories can be viewed and bought here, including sizing information:

http://www.apple.com/shop/watch/bands

Any band that is designed to fit the 42mm watch case will not fit the 38mm Apple Watch.

Ideally, you might consider visiting an Apple Retail Store to find the best fit.