Can someone give me an idiot guide on how to replace an amp speaker?

I am thinking of replacing a Celestion Gold with a Celestion Vintage 30 in my 40W Marshall combo.

I have absolutley zero knowledge and skills in these type of electrical / audio things, so would really appreciate a basic guide (i.e. disconnect that, connect that, etc.). How long does it take and what sort of tools do I need?

Many thanks in advance
You would need a wrench of some sort for sure. depending on how the speaker is wired you may need a soldiering iron. Make sure to get the right impedance when you buy the speaker otherwise you may damage your amp pretty bad.

start by removing the wires from the speaker. if they are connect with terminals you simply can pull them off if the are soldiered on you will need to heat the soldier up and the wire will pretty much just fall out once the soldier melts. note which wire goes to the positive terminal and negative terminal. Usually red goes to positive and black to negative, but it may be different in some cases.

next remove the nuts from around the basket of the speaker. remove speaker and put new speaker in. put the nuts back on; don't tighten them too much you make warp the basket and somehow damage the cone resulting in bad tone or a broken speaker.

now either put the terminal clips on the respective +/- terminal or soldier the wires on the terminals.

turn on the amp and hope you didn't screw up.
Current Gear:
Ibanez rg470
Peavey ValveKing 112
Blackheart little giant head
2 homemade 112 cabinets
Boss SD-1