My PC has 2Gb RAM -- how do I upgrade to 4 or 8.
You remove the existing RAM modules and put new ones in their place, taking care to choose modules that are compatible with your motherboard. Memory manufacturers like Crucial have 'RAM finder' tools on their web sites.
How do I tell if my mother-board can accommodate the increase.
You check on the manufacturer's web site.
After adding the extra RAM will my PC self-adjust.
My PC is running slow lately - would the extra RAM fix this.
If your use of 'lately' means it used to run faster at some earlier time, then extra RAM probably won't make it go faster. You may have a virus or too many programs running in the background.