Hello @Lewis11,
For the security deposit setting click on "Host", then "Manage listings", then "Manage listing" and then "Pricing".
Then scroll down and click the "Edit" button in the "Extra charges" section. Scroll down again until you find the "Security deposit" box, enter the value and click on "Save".
For the cancellation policy setting click on "Host", then "Manage listings", then "Manage listing" and then "Booking settings".
Then scroll down and click on the "Edit" button in the "Policies" section. Scroll down again until you see the "Cancellation poplicy" section and click on the button for the policy you want. Then click on "Save".
For reference the different policy terms are at this link cancellation_policies.
Steve.