You'll need a 64-bit OS to take advantage of more RAM than 4GBs.
What apps do you run concurrently ?
I am multi-tasker with my desktop. I like to have mutiple tabs open with some or all of them downloading simultaneously. See my computer stats down below and let me know if upgrading from 4GB of RAM to 8GB of RAM is going to help me do multiple things at a faster speed. Thanks!
Dell Inspiron 570
AMD Athlon II X4 630 (2.8Ghz,8MB)
750GB Serial ATA 2 HD
4GB DDR3, 1066MHZ (2X2GB,DIM,M)