OP I've copied some stuff I've found on line .
Yes ,take them out of their pots ,and yes the container must have drainage holes ,several in fact ,to stop the plants getting waterlogged/too wet which suffocates and /or makes them rot .
Usually you can make holes in wood or plastic containers ,.
You'll need to buy compost - I think preferably ericaeous .It will say on the bag .
"They will tolerate a moderate amount of shade but are happiest in full sun and well-drained soil
There are lots of varieties to choose from, such as “Springwood White”, “Springwood Pink” and the deeper pink “King George”.
You could plant them with 6in or 8in between them and fill the gaps with spring-flowering crocuses, dwarf irises or miniature narcissi such as “Tete-a-Tete”, “Little Witch” and “Jenny”
Plant heathers at the same depth when you had bought them from nursery or only as deep as the plant’s root ball would only be covered in soil. Heather should not be planted too deep to avoid root rot. Too shallow planting is not good as well.
Start by adding a layer of compost, then arrange your plants.
When you’re happy with the display, fill the gaps with more compost, leaving a 5cm gap between the surface and the lip of the pot.
Containers are best placed on pot feet to ensure excess water can drain away.
Calluna only likes acid (ericaceous compost) soil, whereas Erica is happy in alkaline or neutral soil.
Lightly trim winter-flowering varieties in April after they have finished flowering – follow the contours of the plants using secateurs or a pair of hand shears."