well avg is a huge memory hog , i stopped using it , but if you notice it going slower sounds like you have hidden viruses and spyware , other than that you may be using up too much space in the hard drive and should start deleting crap you dont really need , Also you maybe have too many installed programs , but most of all delete the crap from your hard drive .
If your looking for a very smart program to clean your pc , go to
www.download.com and download a program called Advanced SystemCare its a free program , and it can free up your memory too , when you get it go into utilites and click on SMART RAM then click on GO and choose how much you want to free , i kept on clicking on deep clean untill my ram was back to normal , and it helped alot my pc was heaps faster after that , you can also have the smart ram running in the background and it inteligently frees up memory as you use your pc doing whatever you are doing .