Hi,
It looks like you don’t have permission to write to the directory that WordPress is intending to create the theme directory in. It’s recommended to set the following file permissions:
755 for all folders and sub-folders.
644 for all files.
Hence, make sure that you change folders and file permissions “recursively” to 755 and 644 respectively as it might happen that you have certain permissions for the main folder but the subfolders have different permissions.