You can request to change from full-time to part-time study, but whether a change is possible will depend on a range of factors. The type of programme you are studying and your progress through the current academic year may need to be taken into account. There will be considerations for you, too: changing from full-time to part-time may impact on your tuition fees, student support and (if applicable) visa status.
It is a good idea to discuss your intentions with your programme leader, who will be able to give you more information about the feasibility of a change and the impact it may have. If you would still like to go ahead with the change, your programme leader will be able to help with any necessary paperwork.