You are looking to update the current Terms and Conditions (T&Cs) that appear on your landing page footer links or at checkout.
Head to Event Setup > Settings > Legal & GDPR
There, you will see a field for Terms and Conditions (summary). This will change what is visible during the registration process.
There are also fields for Terms & Conditions (full) and Privacy Policy (full). This will change what is seen on the dedicated pages (which can be navigated through via the footer links). If you add your own T&C or Privacy Policy, these will be added above the original HeySummit policies, but will not replace them.
Do note that Markdown syntax is used to assist with formatting.
Example:
You can read more here about the Cookie Consent Popup and the Require Explicit GDPR Opt-in feature.