Pls have a look at this for more info on setting the memory for your wordpress installation –
http://codex.wordpress.org/Editing_wp-config.php#Increasing_memory_allocated_to_PHP
You will need to modify the wp-config.php file. You can also try this plugin –
http://wordpress.org/plugins/change-memory-limit/
I recommend at least 128MB memory. After activation, you might memory issues again when you try to import sample data. If the above change does not make a difference, pls contact your hosting provider to increase the memory allocated. Let me know if you need further help. Thanks