Having problems changing the default URL to root

I am facing two issues with my wordpress application:
1. I am able to access my wordpress website using http://<my_domain>/wordpress but I want it to be accessed directly by visiting http://<my_domin&gt;. I know there are many ways that are listed on your website but none of them worked for me. one thing that I noticed is that I can achieve the same using wordpress address and Site address fields in the general settings of wordpress, but those fields are greyed out in my wordpress application and I am unable to change those fields, can you please tell me why they are greyed out and how I can activate them?

2. I tried to solve my problem by using the tips given in http://wiki.bitnami.org/Applications/BitNami_Wordpress_Stack#How_to_change_the_WordPress_domain_name.3f Now, for some reason, I am not able to access my site at all. I had taken a backup before meddling with my htaccess and conf files, when my server became unreachable, i simply restored the backup and refreshed my page. But I am not able to solve the problem and I am unable to use my dashboard.

Please help me with this issue. If there is a better place where I can ask these questions, please let me know. Any help would be appreciated.

Thanks,
Shripad Deshpande