You can do either. They are just two different ways to approach the 2-1:
1. Push out the morning A time gently, let LO sleep as long as they like and offer a short catnap to see you through to bedtime. The am nap will gradually get later and later until it's a midday nap and you drop the catnap.
2. Cap the am nap, so LO will take an earlier, longer (uncapped) pm nap. Eventually you drop the am catnap, and bring the pm nap earlier so it becomes the midday nap.
Either way, it's good to leave one nap uncapped (or perhaps capped at 2hrs if necessary) so that LO is used to having one long nap which just shifts gradually. Option 2 is often the best if LO is prone to EWs, or if they tend to refuse even a late, short, catnap. But also consider whether your LO generally seems to prefer to have a long am or pm nap, and what will work best with other activities etc.
The other thing to bear in mind is that there can be lots of developmental stuff going on at this age (crawling, pulling to stand, practising sounds etc) that can interfere with the ability to settle for naps every now and again