Weening a toddler from breastfeeding

Hey ladies! I am currently pregnant while breastfeeding my almost 5 year old. I want to try to ween him off a bit since I only produce milk in one breast, and his sister will need all of that milk. How did you ween your toddlers off? Everytime I bring up stopping, he gets upset and cries. I feel like I’ve gone too long and can’t stop.

Please give me some tips