according to MSI you can have 16GB of ram in two sticks of DDR3 133. it's $23, there's no reason not to get a set of two at that price even though you already have one. who knows what the CAS latency is on the one you have and both sticks need to have the same latency anyway, so go ahead and do both if you want to upgrayedd the ram.

you could easily replace the sata hard drive with a sata ssd. here's a 1tb one for $72. you could go less and save some money.

the thermal paste is the hardest part, you gotta take some screws out, yank the heatsink, clean the old paste off and reapply new. here's a video of someone taking it apart. assembly is the reverse of disassembly. i use alcohol and paper towels to clean cpus and heatsinks. here's some thermal paste for $6. i use cheaper and shittier stuff because most of the stuff i work on isn't as high temp as computers. it ought to be fine.