The Windows Experience score is a number that takes your computer's CPU, memory, hard disk, graphics, and gaming graphics capabilities into consideration and translates it into a number between 1 and 5.9 (with 5.9 being the best possible score). Each of these considerations is given a sub-score and the lowest score then becomes the computer's Windows Experience Index score.
Once you have your score, you have an idea of how your computer rates. Low scoring computers may be fine for basic computer tasks but will be ill suited for demanding applications such as gaming or video editing.
Since the lowest score becomes the base score, the easiest way to increase your Windows Experience score is to raise the lowest one. For example, if your CPU, Memory, and hard disk are rated fairly high, such as in the 4.5 or above range, and your graphics and gaming graphics scores are down in the 2.0 or below range, then improving your computer's graphics capabilities will improve your overall score. In this case, upgrading the graphics card should raise the computer's base score.
Before you go out and buy a new graphics card, consider whether doing so is meaningful or not. For example, if your computer performs just fine as is, then an upgrade may not be necessary. If all you do is send e-mail messages back and forth and do your banking online, then you don't need a high end graphics card. If your computer is always running low on memory, then adding more memory may be a better choice.
Keep in mind that the Windows Experience Index score is a rating that measures your installed hardware, not actual performance. You may have a high-scoring computer that is inexplicably slow. The hardware is in place, but the system hangs, crashes, and crawls. Even the best equipped computers can get bogged down with clutter - and there isn't an index that rates actual performance.
While upgrading hardware will get you a higher Windows Experience Index score, it won't necessarily solve malware-related slowdowns or a cluttered registry. Instead, make sure to scan your computer for viruses and spyware regularly and clean out the Windows registry with a reliable registry cleaning product such as RegCure. Your score won't go up, but your performance will.