You can directly download themes from your ssh or putty.
1) Go to themes directory of your drupal installation. E.g:-
cd sites/all/themes
2). Download archive using wget command:
wget http://ftp.drupal.org/files/projects/acquia_marina-6.x-2.0.tar.gz
3). Uncompress archive:
tar zxvf acquia_marina-6.x-2.0.tar.gz
4). Delete/Remove archive:
rm -rf acquia_marina-6.x-2.0.tar.gz
5)Confirm your theme is there:-
ls -a
Also check and enable it from:- admin/build/themes
Note: the theme acquia_marina-6.x-2.0.tar.gz is taken here as example please check the current
version and or substitute with your preferred module. You can do same for themes also.