Next you could remove the screws and the covers for the various bays - RAM, HDD, etc.
These are the screws on the outside - there are a few others to remove once the covers (above) are removed. Please also note that the one in BLUE is for the optical drive. It's positioned so you can remove/replace this without disturbing anything else.
Once the covers (and hard drive) are removed here are the remaining screws. See below for removing the hard drive.
To remove the hard drive there's a single screw in the top left corner from the shown orientation.
Remove it and then slide the drive to the left then lift up.