UPDATE Pieris Poorly?

Hi all you wonderful, knowledgeable people. I've removed some of the existing soil and added about 3 kg of ericaceous soil as advised and can see an improvement already I've yet to purchase some feed though.
Someone suggested repoting it! The existing pot is 22" deep and the plant is 33" high so it will be a massive job, is it absolutely necessary?
When I bought it 8 years ago it had been in a courtyard with limited sunlight but was healthy so I positioned it in semi shade. However my neighbours Pieris, which is in full sun, is splendid. So when mine recovers is full sun the best place? Once again TIA

 

It’s not so much the height of the pot, but the width that caught my eye. I would have done both at the same time, that is, remove some of the old compost and pot it on. That said, since you have replaced some of the old compost, I’d wait and allow the roots to occupy the new compost before repotting. Keep it fed (as per instructions) and just keep an eye on it. Full sun or part shade, either is fine I think.

 

Thank you Freddy