Yes, it easy to remove the HDD and you can upgrade it. One srew to remove the HDD and probably about four to remove the caddy.
Here is IBM describing the removal of the drive. Of course they don't say that you should lift the lid for the LCD, but you should, otherwise the top part of the plastic catches the overhang of the LCD and makes it harder to remove. If you want the specs on your HDD, just remove your HDD and go to the manufacturer's page to see the specs. I didn't bother to look, so I don't know if your computer will take a drive taller than 9.5mm, but most drives out today are 9.5mm so it won't be hard to find a suitable upgrade.