Couple things will help me. First off I would like you to download and install then run this http://www.piriform.com/speccy/download . THis will show us what you have in there. Give us a better overall picture. After that I would like you to go here http://speedtest.net/ and click Begin Test. PAY ATTENTION TO WHICH BUTTON YOU CLICK. Click Begin Test. When it is done please click on share then click on copy. NOT FOR THE FORUM. Just click copy for the URL and then paste the link in your add details section along with a copy and paste of your Speccy summary page. If you do it right we will see a list of info like this
Operating System
MS Windows 7 64-bit SP1
CPU
Intel Core i5 2500K @ 3.30GHz 29 °C
Sandy Bridge 32nm Technology
RAM
8.00 GB Dual-Channel DDR3 @ 665MHz (9-9-9-25)
Motherboard
MSI P67A-G43 (MS-7673) (SOCKET 0) 32 °C
Graphics
DELL 1704FPV (1280x1024@60Hz)
COMPAQ FS7600 (1024x768@85Hz)
1280MB GeForce GTX 570 Classified HD (EVGA) 38 °C
Hard Drives
78GB Western Digital WDC WD800JD-00MSA1 ATA Device (SATA) 20 °C
977GB Seagate ST31000528AS ATA Device (SATA) 25 °C
Optical Drives
ATAPI iHAS124 Y ATA Device
Audio
Realtek High Definition Audio
and a link like this http://www.speedtest.net/result/1581442835.png . We will then be able to have a better idea what's really going on and the best way to go about upgrading .We also need a budget. Lastly what games are lagging?
EDIT: WOW!!!! That CPU is hot.
Well with the info we can rule out your connection. That is SCREAMING fast relative to most of the residential connections. Suddenlink, Comcast or Time Warner is probably your provider. Your ping(43ms) is low enough so that it won't affect online gaming so regardless of the game your connection is fast enough so that it won't negatively affect your gaming.
Yes it is sorta your RAM's fault. That is DDR2 RAM which is slower than modern DDR3 RAM. This however is decided by your board so unless you can afford a new computer we will have to deal with that.
Do a search for "AMD Athlon 64 X2 4800+ 2.5GHz 2x512KB Socket AM2 Dual-Core CPU" over at Amazon. That is an archaic CPU but faster than your current one and if you try and buy a brand new AM2 right now they will be insanely expensive.
Your CPU is hot but not in the dangerous area of hot. However unless you are doing some MAJOR gaming while your asking that question your CPU should be a LOT cooler. With a stock cooler maybe around 50°C. You didn't give a total budget so take a look at these AM2 CPU coolers http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&N=40000574&IsNodeId=1&Description=am2%20cooler&bop=And&Order=RATING&PageSize=20 . Those will keep your CPU cooler and that usually equates to longer life.
Below are some choices. I would reallystay away from higher end cards like the 570 even if you do have the money because that CPU will hold back the gfx card. A system needs to be balanced and unless you upgrade your CPU as well your upgrade option will be more limited.
http://www.newegg.com/Product/Product.aspx?Item=N82E16814150560
http://www.newegg.com/Product/Product.aspx?Item=N82E16814103122 With that $30 MIR this is a good deal.
http://www.newegg.com/Product/Product.aspx?Item=N82E16814130696 has a $20 rebate and it is superclocked which is VERY nice.
I really wouldn't go too much higher. Your old dirt road RAM and your CPU will hold up traffic.
http://www.newegg.com/Product/Product.aspx?Item=N82E16817207013&Tpk=550W%20PSU%20XFX is more than enough SAFE and EFFICIENT power to power your card and the rest of your system. I wouldn't go ANY less than this power supply. Absolute minimum for those cards is 500W so that 550W will be perfect.
Should you opt for a new computer please do NOT go for a hex core . The Pheom x 6 or FX 8 core need to be avoided like the plague when gaming. The 980 BE will be plenty powerful enough and is more task oriented than the hex or 8 core processors. http://www.anandtech.com/bench/CPU/2 is a good site to compare processors side by side . They show many tests including many gaming benchmarks.