You will need to formally advise your line manager of your new role, and HR will automatically move you to your new role on receipt of the appointment panel form from your new manager. You will be expected to work your notice period. However, sometimes your new manager may be able to negotiate a shortened notice period with your current manager, and sometimes a transition period is agreed, e.g. two days in your current role and three days in your new role for a period.
Any annual leave remaining for the current leave year, will transfer with you to your new department. If you have lots of leave left this may seem unfair to your new department, but this is usually balanced out across the University over a period of time, with the internal movements of staff.
Please note annual leave entitlement is different for each group of staff (Professional Services, Academic and Senior Staff) and therefore your entitlement may change if you are moving from one group to another. This will be detailed in your new contract.