According to picture I see here at this link it looks like a standard case with a faceplate that had spring loaded doors.
http://computeuk.co.uk/shop/Packard-Bell-UTOWSUNStep 1 would be to remove power cord from system.
Step 2 would be to remove side cover
Step 3 would be to locate the front face plate locking tabs... you will need to get the faceplate to pop off the front of the case. It might have tabs that hinge pivoting or it might require undoing multiple plastic tabs carefully for the face plate to pop off. Be careful as these snap and break easily. They might be labelled with an arrow as to which way to move them to unlock them. They grab into the steel case facing locking them in. They need to be bent one way or the other to unlock them. But too much force breaks them.
Step 4 would be with face plate off, remove the IDE or SATA cable and power cables from rear of the drive inside the case.
Step 5 would be to remove the screws that mouth this drive. Some cases have 2 on the exposed side with a track on opposing side, other cases have 4 screws 2 on each side and require the other side panel to also be removed to get to them.
Step 6 pull carefully on the DVD drive from front of computer and pull it towards you when you know all cables have been detached.
If its an IDE drive and your putting in another IDE drive then you will want to match the Master, Slave, or CS ( Cable Select ) jumper settings on the rear of the drive. If its SATA its even easier you just simply plug into the drive with sata power and communication cable. IDE is a wide ribbon cable and SATA is a narrow cable about 3/8" wide.
Once drive is mounted inside add screws to hold it in place. Then connect power and communication cable for IDE or SATA. Add face plate which should snap back into place. Add side covers. Add power cord and boot it and it should work.
