Yes. Almost all notebooks that are sold can be upgraded in one way or another. The most common upgrade would be to add more RAM or a larger/faster hardrive. Optical drives can also be upgraded in many notebooks. Some of the more expensive, enthusiast notebooks also have upgradeable video cards.

Many notebooks ship with 4200 rpm hard drives, these can be a bottleneck, slowing down any processes that rely on disc access.

As with any upgrade, always check with the manufacturer before attempting to upgrade any components.