Practice your reading frequently. According to the American Psychological Association, new research shows that "working" memory capacity can expand if a person practices. It may be tempting to avoid reading if you find it difficult to retain information, but you are not maximizing your potential by doing this. It is important to choose reading material that you are really interested in, rather than something you feel you ought to read. Avoid dense reading that requires intense concentration.
Take your reading one step at a time. Break a book, or a chapter into smaller sections. You may find it easy to read just one chapter, by breaking it into pages, and then into paragraphs. Stop, at the end of each paragraph and recap what you have read. Many libraries and book shops stock "easy-read" books that abridge well-known publications. These can be less daunting if you have difficulty with your "working" memory.
Use audio books to reinforce your reading. This can help to make more sense of what you have read and can help you to remember. If you are reading for academic purposes, take notes as you go, and read these over immediately afterward. Take frequent breaks and do other activities that improve the concentration, as concentration is linked to memory. Crossword and other word puzzles help you concentrate in a less pressurized, more enjoyable way.