Hello Cynthia de boer,

Sorry for late reply to this,
Please find your answer in your queries below.
1. How can i disable the option that users can change there vote in the poll?
>> You can disable it from your backend > Easydiscuss > workflow > general > voting
>> Check my screenshot below how to create poll in your question or reply.

2. And is there an option that the votes remain secret until the voting period is over?
>> Unfortunately we do not have this in current system.