how are you uploading the theme? If you are doing it via sftp/ftp, you might need to change permissions on the newly uploaded theme like:

sudo chown -R www-data:www-data /var/www/

Yes via sftp.
How do i change this? Can you explain me step by step @sierracircle

do you have access to ssh to your server? If so, then you just run that command (assuming your web-folder is /var/www):

sudo chown -R www-data:www-data /var/www/

that should do it.
If you do not have access to ssh commandline, then some sftp clients will let you change permissions, but it is different on each client, so I cannot give instructions for that