how do I change my icloud security questions if I can't log in?

Hi Rob096,

welcome to the Apple Community.

Try these Apple Support links:

 What’s happening with your Apple ID?  

( Click on "Forgot security questions" and follow the instructions)

https://getsupport.apple.com/?caller=kb&PRKEYS=PF23&locale=en_US 

Tips for choosing security questions:

https://support.apple.com/en-au/HT201303

All the best :-)

You can't login in with appleid .apple.com as answers for three respective questions are incorrect , however you know Apple ID and its password .

Convert the secondary authentication account into 2FA Two-factor authentication for Apple ID - Apple Support

Get a verification code and sign in with two-factor authentication - Apple Support

Note : you can't change security questions and answers ( as answers for respective questions are incorrect ) .