To exhange the armour set for the armour itself, right click on a Grand Exchange clerk and click the 'Sets' button. Then right click the set you want to exchange, click exchange.
Drast
Click Set-up cannon stand. Your RuneScape character will automatically set up the rest.
no and there probably wont be
Torva set
Ask your parents, or whoever set up the parental controls, to enable RuneScape.
You can buy it on the Grand Exchange.
Depends in what you mean by multiplier
Yes you can own as many cannons in runescape. But it will only let you set out one cannon only.
There is no such armour in RuneScape. If such a set existed, it would a) exist on the Grand Exchange, and b) have an article on the RuneScape Wikipedia (both official and unofficial Wikis).
in either the grand exchange or you can make one
if you didn't have recoveries set then you cant.
meow
I don't think there is such an option.