if he keeps his graphics card no, the board and memory aren't consuming much and the processor will probably have a higher tdp if he gets an amd phenom but lower if he gets an intel core i5/7 and in both cases the processors don't consume much compared to the x2 4400+ or any older processor (the power consumption nowadays compared to a few years back is most likely the same if you compare the products from the same range, the bigger change is the new instructions and cables needed for power supplies aswell as the importance of 80+ label)
as people suggested this is a waste of money to upgrade on a socket 939 which is dead now
your best bang for buck platform would be to go on an am3 socket with an athlon x4 (you could get an athlon x2 and unlock the cores to get a x4 but since you don't know much about computer forget it), 4gb of ddr3 memory at 1333mhz (pc-10600) and a decent quality motherboard
do you know the power of your power supply and it's brand? we also need to know what is your video card, to see if it's necessary to change it and if you do to change the power supply aswell (for a standard upgrade to a quadcore processor and a mid-end graphics card you'll have no problems with a 500W good branded powersupply (corsair, seasonic, thermaltake, antec, enermax, be quiet, fortron, fractal design) and it'll be better to have a 80+ power supply which ensures you to not waste power during the transformation from your domestic electric current to your pc electrics needs)
here's what i would get for a good bang for the buck situation:
processor: amd athlon x4 620 (am3) = $90
Newegg.com - AMD Athlon II X4 620 Propus 2.6GHz 4 x 512KB L2 Cache Socket AM3 95W Quad-Core Processor ADX620WFGIBOX
memory: corsair value 2x2gb ddr3 (1333mhz/pc-10600) = $93
Newegg.com - CORSAIR 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1333 Desktop Memory Model CMV4GX3M2A1333C9
mainboard: asus m4a785td-v evo (am3) = $100
Newegg.com - ASUS M4A785TD-V EVO AM3 AMD 785G HDMI ATX AMD Motherboard
for a total of $285 that would be a solid, quality and futureproof upgrade
but we still need to know what is your graphics card to see if you change it and if you need a new power supply
and also what would be your budget for such an upgrade