repair in future. But in this case, the memory would be more expensive.
  If quality warrant has expired, then OK, just take it to IT shop and do it. As the 512MB RAM replaced, you could collect it/them yourself, or just sell it/them out.
3): If you want to update your memory, then please notice that whether the memory has compatibility problem, so you should buy the original same brand and model, (I even met the situation that the memories of same brand and same patch have incompatible problem). So you’d better change the original memory, otherwise, incompatible problem may occur easily, then the laptop could not start up. Hope this could help you!