Change write permission on .htaccess file in sites/default?

I am new to Drupal (and building my own site). I have installed Drupal 8.2.5 at my hosting provider with Filezilla. When I access my site, you can’t see any pictures (or colors) only text. In my previous installed version (which got lost because I forgot to back-up the database) my hosting provider commented out a few lines in .htaccess in the directory sites/default.
How can I do that myself? I tried downloading the file to my computer, altering it and try to upload, but I get an access denied error.
Thanks in advance,

Cheers Tom.

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