Well, this machine is a somewhat old (could be worse) Emachine (XD, yes I know) and as you can guess, it needs an upgrade.
I believe this is our motherboard:
Motherboard
Compatible processors
And these are a few CPUs that I might like:
CPU1
CPU2
CPU3
As far as I’ve read, those processors are compatible, is that correct?
I’ve never ever replaced a CPU before, so is there any extra factors I need to be aware of? (I know about the thermal grease, and I ordered some antistatic gloves too) 
Our current CPU is single core, the processors I want are duel core, will I have to make any BIOS changes or anything like that?
When there’s a 2 Gigahertz processor, but it’s duel core, does that mean it has a total of 4 Gigahertz processing power?
Is there anything else I should know about changing my CPU?
Thank you very much for your time!