Transplanting bonsai to bigger pot (what soil)?


I just acquired a port Jackson fig bonsai that is apparently 30yrs old. I wasn’t expecting to get it, but I want to do my best for it.

Its only in a really small pot, like 1ft long 6’’ wide, and like 4’’ high. I want to put it into a very big pot, like a half wine barrel so it can get much much bigger. But I don’t know how to do it.

Am I supposed to cut the roots or something or can I I just crack open the pot and put it in there? Also, what sort of soil should I use (I tried looking and its all way to confusing all the different types). Like can you look at this selection and literally tell me what one to buy? (like I said I really don’t understand about the soils)

Thanks that’s all for now I can think of