The actual upgrading is easy and so is finding the right RAM. Go to Crucial click here and use their RAM finder to find the right stuff.
It's unlikely to be 224mb though - RAM comes in multiples of 64. i.e. 64, 128, 256, 512 and then 1gb.
To install the RAM open the flap at the bottom of the lapton and insert the memory card at an angle and then snap it down into place. The memory will come with illustrated pix anyway.