This happens because of max_execution_time, memory_limit and maybe because of upload_max_size limit. Those are server settings that can be changed. You can ask the host provider to increase the limits or you can change them in php.ini file:
memory_limit = 256M
upload_max_size = 64M
post_max_size = 64M
upload_max_filesize = 64M
max_execution_time = 300
max_input_time = 1000
or in .htaccess file:
php_value memory_limit 256
php_value upload_max_filesize 64M
php_value post_max_size 64M
php_value max_execution_time 300
php_value max_input_time 1000