Hi Emx,
It's really easy to switch your degree, providing you have the requirements for both. I think you can change your degree until the end of 2nd year, so you have time to choose. The only thing to be careful about is you will have to sit the modules that you haven't done if you switch over.
So for example if you were accepted into Cons. Bio. & Management and your 3 modules in first semester were: Practical Skills, Building Planet Earth (Geology) and Cell Biology. Then after first semester you wanted to change to Ecology and the 3 modules from the first semester were: Practical Skills, Cell Biology and Our Blue Planet. As you are entering semester two, you will have already done Practical Skills and Cell Biology but you didn't do Blue Planet. So, you will need to take that module sometime at a later date.
I hope that makes sense. If it's too difficult to understand, message me and I will try to explain it better.
But yes, changing degree (as long it's similar to what you were doing) shouldn't be too difficult.
Calum