If you have an FTP program with access to your webspace in hosting server
then you can browse your files/folders.
Most FTP programs can change permissions.
With the one I use ( FTP Surfer ), I just right click at folder
and get a menu for changing folder permission.
At many webhosts you have a Control Panel login for you webfiles.
Also the file browser feature in such a control panel
should be able to change permissions.
Think this case you have to change permission on the folder itself.
So you can perform upload and get correct permissions on your images.