I've firmed KCL for Economics and very little accommodation is left, when I booked last week I only had a choice of 4 rooms across 2 halls so I booked one with the idea of changing when something else became available. The accommodation portal is now saying that changes are not allowed due to the lack of availability. You may need to accept anything you can and change when more becomes available, probably on results day? Although be sure that what you do initially choose is something you'd be happy to stick with. When I researched accommodation I found a video of a med student reviewing Julian Markham, he said this is popular with other med students due to it's location, This is what I booked and it looks great but not cheap!