Can I put my Pieris Japonica in a bigger tub? If so any tips please

Yes, you can. If you're planting it on its own, don't use an enormous tub though - it will eventually grow and need potting up into a bigger container, but initially, something 2/3 times the size of the container its in currently will be fine. Get some ericaceous compost (specially for acid loving plants, available at the garden centre). It will grow in multipurpose, but prefers acid conditions, so will do better in the ericaceous. Pieris is a woodland plant, so likes dappled shade, so your 3 hours sun should be fine, unless its midday sun, then you might find the leaves burn a bit. And keep it watered, make sure there are drainage holes in the bottom of your container.