Very Cheap CPU Upgrade option might be possible to upgrade to a Phenom Quadcore like this one, but we need to know what you have for hardware to ensure that its a match or not to what your system will support. This here is a Phenom x4 9550 2.2Ghz
http://www.ebay.com/itm/AMD-Phenom-X4-9550-Socket-AM2-AM2-CPU-HD9550WCJ4BGH-2-20GHz-/332359990161?epid=74121847&hash=item4d6232fb91:g:vwEAAOSw2b1Zo7Y7While I agree with mark on the SSD upgrade makes quite a difference and is easier, from my experience with the Radeon HD 3000 to 5450 GPU's in systems that I own, the 3000 series radeon is a weakling and for around $30 a brand new video card could be added to make better performance with streaming video and games.
My Athlon 64 x2 4450B 2.3Ghz which is similar benchmark to your CPU I have paired with a Radeon HD 5450 instead of the Radeon HD 3000 which is onboard. There is quite a difference between the HD 3000 and HD 5450 and the 5450 and 6000 series radeon video cards can be picked up for around $30 if thats something that interests you.
Biggest thing is whats your application for this system so we know what exactly needs to be sped up... such as I mentioned prior if its internet is slow its probably just that internet is slow and not so much the computer etc.
Lastly on the SSD subject the best part of that upgrade is that say you do that upgrade and your system will be faster to boot and load programs, but applications remain the same speed in CPU execution, you eventually find yourself needing a better system for some reason, that SSD can migrate forward to a newer build so its not wasted money. Video card also can migrate forward to a newer build as well. But for maybe $10 you can more than double the processing power by leaping forward to a high end CPU such as the Phenom x4 9550 2.2Ghz vs the Athlon 64 x2 4000+ 2.1Ghz. *Note: single threaded applications will run about the same but applications able to tap into multithreaded execution will be more responsive. Single threaded applications would only run 100Mhz faster in execution due to the 2200Mhz vs 2100Mhz difference unless able to make use of the extra cache that the Phenom has in which there is 2MB of L3 cache and your current CPU doesnt have any L3 cache.
Here is your current CPU for specs etc:
https://www.newegg.com/Product/Product.aspx?Item=N82E16819103774Here is what you might be able to upgrade to cheaply for specs:
https://www.newegg.com/Product/Product.aspx?Item=N82E16819103251If able to upgrade to this and confident in your ability to perform a CPU upgrade or have someone else who is around who might be able to help hands on, for $10, I'd perform the upgrade. But dont purchase this just yet, we need to make sure your motherboard would handle this and verify that cheap upgrade to older hardware makes sense or not.
Here is your current CPU benchmark = 1042 =
https://www.cpubenchmark.net/cpu.php?cpu=AMD+Athlon+64+X2+Dual+Core+4000%2BHere is the Phenom x4 9550 benchmark = 2549 =
https://www.cpubenchmark.net/cpu.php?cpu=AMD+Phenom+9550+Quad-Core2.5x faster benchmark, but that doesnt mean necessarily that stuff will launch 2.5x faster, however the SSD would make stuff launch faster by its ability to feed the RAM a faster dump of information than the Hard Drive can.