Can I upgrade any parts in this HP Compaq 6720s

george bartlett, running slow can be caused by a fragmented hard drive, to many processes on start up as well as viruses and malware. I'd start with some necessary housekeeping. You want to check your computer for Viruses and Malware first. Use programs of your choice, I prefer Avast and Malware Bytes. If your machine is clean, you want to check and see what is going on in the background. I use "What's my computer doing" to check on that. See what it is loading when it starts up. MSConfig should show you that. also, check the answer by "Gary" on here, makes a lot of good points on what to do. Once you are satisfied that you eliminated all unnecessary processes, defrag your hard drive. Then you check on your hardware. The most important thing here will be memory and storage. Make sure the fan works, and that the airvents are clean and free of any obstruction. One of the biggest improvement you can have is added memory. Your computer can take up to 4GB of of 533-MHz or 667-MHz DDR2 SDRAM modules; go with the 4GB. I believe the standard size hard drive is a 250-GB 5400 rpm SMART SATA Hard Drive, replace that with a bigger drive, (think 750GB +). Those updates will serve you for a while longer and are not very expensive. Hope this helps, good luck.