There isn't really a lot of point repotting it now. It is very likely to wilt and sulk with all that lush foliage. Dahlias flower in mid-late summer and the first hint of frost will kill off the foliage anyway. At that point you need to dig up the tuber and store it cool, dark and dryish (but not desiccated) until it's time to replant it next spring. However, if you live somewhere that doesn't have cold winters and have a spot with free draining soil you could plant it in the ground and leave the tuber there over winter.