Usually to cancel a policy where the bank has a hold over for a mortgage you need to give the bank the new policy and get their permission then (letter of no further interest) to cancel the existing. Then you send that to the Irish Life together with written instruction from you and anyone else on the policy cancelling it.
Now that's the way it used to be unless technology has taken over and there is a shorter way such as bank advising IL direct or something, I'd say ask the bank.
Of course you could just cancel the direct debit but if the bank has an assignment on the policy then IL will contact them and then you'll get a letter about your lack of life cover etc etc so if you are taking out a new one you may as well just do it the right way.