Hi Wadey,
Windows installations can sometimes slow up especially if there hasn't been a great deal of maintenance. Using something like Ccleaner and defragging the hard driver helps no end as does keeping the system updated.
Try using Ccleaner to clean up old files:
This will tell you how to use the defragger:
The upgrade will place all your files and folders into a folder marked Windows.old although whether this will speed up the system really depends on how the upgrade goes. some users complain their systems are slow after the upgrade but if that's the case simply wait until your new key is issued (usually 24hrs after upgrading) and then use that to perform a clean install which will really clean out the crap..