To remove website field from all comments and user profiles in a wordpress powered site you need to run the following mysql commands:

To Remove Website Field from User Profiles

First you need to login to the command prompt of your virtual private server. Then execute the following commands.

mysql -u root -p
show databases;
use dbname;
show tables;
describe tableprefix_users;
select count(*) from tableprefix_users where user_url!='';
select user_url from tableprefix_users where user_url!='';
update tableprefix_users set user_url='' where user_url!='';

To Remove Website Field from Comments

show tables;
describe tableprefix_comments;
select count(*) from tableprefix_comments where comment_author_url!='';
select user_url from tableprefix_comments where comment_author_url!='';
update tableprefix_comments set comment_author_url='' where comment_author_url!='';