To change the hydraulic fluid in a Massey Ferguson 275, you will first need to drain the fluid from the reservoir. Disconnect the line that runs from the reservoir to the hydraulic pump, and drain the fluid into a container. It is also important to make sure that any air bubbles have been removed from the fluid. Once the fluid has been drained, replace the line and refill the reservoir with new hydraulic fluid to the appropriate level. Use a lint-free cloth to wipe down any dirt or debris from the outside of the reservoir. Finally, start the Massey Ferguson engine, and check for any leaks in the hydraulic system.