I have an FTP account(admin) and I would like to know if its possible to restrict it so that it cannot be deleted or the password cannot be changed.

I have created a website for someone and want to have access to it in the future.

If you do not own access to the website's control panel, then yes, the password can be changed.

I think this is not a matter of access but of trust. Make sure you have a decent contract.

Someone else is expected to work on the content. I don't want him to delete my account or change my password. I completely trust the guy but don't know if the new developer will edit my account or create himself a new ftp account hence the question.