Hi @Stella40
Only the terms and conditions that were in place when your guest booked will stand.It wouldn't be fair to guests to book at one price and with one set of conditions only for a host to be able to change it to suit their own requirements at will.
I am glad that you have decided to honour the bookings that have been made.
When you are reading up on roles and responsbilities as a host, please pay careful attention to
1. Host cancellations and host cancellation policies
2. Deposits
3. What to do if a guest damages your property or behaves badly - how to claim through host guarantee or deposit.
4. Importance of house rules - make sure you cover no additional guest other those who have booked to be in the property, use of kitchen, cleaning issues and noise.
5. What to do if a guest turns up with more people than have booked/animals/children
You can find out about these areas by using the help section on Airbnb's website and by reading the useful community guides you have already been given links to.
p.s. I would also review your photos and ensure clear, well lit shots of the bedroom with the bed properly made up and the bathroom are shown early on in your listings rather than halfway through.
Good luck