The 18 districts will become 10 districts (to correspond to 20 LegCo seats, 2 per district). I believe more details will be forthcoming (exact boundaries) but I strongly believe that there has been an effort to gerrymander districts to break up pan-democrat strongholds and mix in more pro-government votes - like how the majority party in the US redraw districts to their advantage after every census (10 years).
If you need an explainer: https://www.youtube.com/watch?v=Mky11UJb9AY