Using FTP you can try increasing the memory for PHP and WordPress in several different ways:
1) You can edit the memory_limit line in your php.ini (if you have access to that file) to increase memory to 64M:
memory_limit = 64M;
2) Try adding the 'define" line below in your wp-config.php file a few lines of white space below the opening
<?php in the file:
3) If those don't work, try adding this line at the top of your .htaccess file:
php_value memory_limit 64M
If that doesn't work or throws a "500 Internal Server Error", delete the line from .htaccess.
If none of those work, your host probably doesn't allow memory allocation overrides. You're stuck with what they give.