i wanna change the speakers on my peugeot 206. Do i need to upgrade the speaker cables?

of course not

No you dont need to

But it would be better if you are buying a good pair of speakers

because the speaker wire loom is like bellwire

but if you are not to bothered what it sounds like then no need

but while you have the speakers out you might aswell change the wire

if you want to change the speakers which are fabricated in doors, no you don`t need to change the wires but if you want to add speakers behind the back seats( and disable the speakers in the back doors) you have toe use new wires.

you may but that would make no difference you could hear

Not necessary at all. The speaker wires are added during factory construction. They are under the dash, through the door frame, and then inside the doors. Very difficult to do the same thing yourself.

The rear speaker wires go under the carpeting, and maybe worse..on some cars they are through the roof frame and down the inner walls at the rear.
So why add so much work for yourself to have no extra quality of sound.
You can relax, sir.