My availability has changed, I can do more/less shifts now.
To edit your availability, go to your Profile and select Work Preferences, then Time Availability. Tick/untick your availability and press "Apply and return to profile" at the bottom of the page when you are finished to save your changes. When you are browsing shifts, the available shifts will refine to suit your availability.
If you are already booked onto a job and your availability has changed, you can cancel any shifts in the app 24 hours before the shift is scheduled to begin.