How to actually cancel my vodafone contract?

I don't mean cancel it early or anything, I simply mean cancel it normally, because my contract is due to end soon and I'm pretty sure Vodafone say you can cancel/ upgrade your contract 90 days before the end, so how do I actually go about doing it? Because I can't seem to find any option to do it on their website. (I have the iPhone 4 btw if that makes any difference at all)

If you go into your account online, there should be an upgrade option. Selecting that will give you the earliest date you are eligible for an upgrade.

Failing that, phone Vodafone and ask them to check it out for you.

Early upgrade is one thing - 90 days before is common
Notice of cancellation, is another - that is usually a minimum of 30 days before end
however, many companies will not accept very early notice to cancel eg more than 40 or 50 days

in anycase, most people will move their number to end the contract with a PAC code, that way you don't need 30 days, you can just move when the PAC code is handed over to the new network, There's then a refund of any unused bill. You don't get that if you simply 'end' the contract with the 30 days (and lose the number as well).

So I suggest getting a PAYG SIm from another network
asking for your PAC code in the last week of your contract
and giving it to the new PAYG network to be used on the last day of the contract (you can tell them which day to move it on, it does not have to be next day)

Just phone to 191 and go to accounts/account changes
they will sort it