Why can you remember a phone number but not 10 random digits?
Your memory does not hold more by trying harder - it holds more by grouping smarter.
Working memory can only juggle a handful of items at once. The trick is that one slot can hold a whole meaningful group, not just a single item. Bundle loose pieces into chunks you recognize, and the same small number of slots suddenly carries far more.
0901 234 567 is ten digits, but you store it as three chunks, the same way you remember a friend's number without sweating.
You expand what you can hold by grouping raw items into meaningful chunks, not by forcing in more loose pieces.
When you study or memorize anything, group it into meaningful clusters first - that is what lets a short list of slots hold a long list of facts.
Chunk = turn many small pieces into one box, then carry the box.
Learn the idea and practice English at the same time.