At first, a Dell Optiplex 755 computer will probably be able to handle any software programs you install, but eventually you may find that the system specifications will fall behind the technology curve. You can remove individual hardware components inside the Optiplex 755, such as the hard drive or RAM modules, and replace them with new components. To get inside the computer case, you will first need to unlock and remove the side access panel.
Close any files that are currently open on your Dell Optiplex 755 computer. Save any data you absolutely need to an external storage device in case there are any problems while you are working inside the computer.
Power off the Dell Optiplex 755 computer. Reach behind the case and unplug the power cable. Remove each of the cables for the other attached devices such as the monitor, keyboard, mouse and printer.
Place the Optiplex 755 case onto its side on a flat and stable work surface. Touch your fingers against one of the unpainted metal tabs on the back side of the case to release the static electricity in your body.
Find the plastic release latch located at the top end of the far left edge of the side access panel. Grab the latch and slide it out toward the left.
Lift the side access panel upward to unlock its internal metal tabs. Pull the panel off the Optiplex 755 to access the internal hardware components.
To replace the side access panel, line up the metal tabs on the underside of the panel with the locking holes on the top and bottom edges of the case. Set the panel in place and then slide it to the right to lock the plastic release latch in place.