Koodo Community

Will my plan have to change if I buy a new phone ouright?

I have an older Iphone and want to buy a new one directly from Apple. I am unable to find concrete information regarding whether I will be forced to upgrade my existing plan. I hope someone can help shed some light on this. Also, will I need a new SIM card? I'd be coming from an Iphone 4 and likely getting the 6 (maybe 5s?). Thanks!