How to open and upgrade the ram and hardisk.
PC laptops are usually pretty straightforward for HDD and RAM upgrades. The RAM should be accessible from the underside of the computer. Before doing anything, take the battery out. There should be a lot of small screws and vented covers on the underside of the laptop. One of those will be the RAM, not sure where it is for your exact model. Once you have removed the memory door, replacing the RAM is a pretty simple procedure that involves undoing a couple clips, and snapping the new chips in.
As for the HDD, it will be a similar procedure. There should be another cover on the bottom of the laptop (or possibly the side, such was the case for my old Dell Inspiron) that holds the hard drive. One the hard drive is out, take the bracket off, and attach the bracket to your new HDD.
We don't have any guides submitted for your model yet, but hopefully this Acer Aspire 5100 repair manual will give you a good starting point. You can also document your procedure and make a couple repair guides!