Creating a duplicate site for testing theme changes

Hello,
I am new to WordPress and to these forums so apologies if this is not the correct forum for this question. I have a good working knowledge of developing websites using HTML, php, cas, MySQL, etc. But I have been asked to make some changes to an existing website that has been developed using WordPress and the X theme.
I can play with changes in the theme settings and preview this, but I’ve been told that if I save anything, this will immediately be live on the site.
I need to be able to play with some ideas for a new look / rebranding, so need to be able to save these changes somewhere other than the main live site so that I can present some ideas for approval.
Is there a simple way to set-up a duplicate copy of the site that I can use for trying out some new ideas?
I have FTP access but don’t yet have full access to the hosting account.
Any suggestions, appreciated.
Thanks
Phil

• This topic was modified 6 years, 6 months ago by Jan Dembowski. Reason: Moved to Fixing WordPress, this is not a Developing with WordPress topic