First, login as root and enter mysql

 [root@e-smith /root]# mysql

 Welcome to the MySQL monitor. Commands end with ; or \g.
 Your MySQL connection id is 2 to server version: 3.23.32

 Type 'help;' or '\h' for help. Type '\c' to clear the buffer

Next load the database you wish to use, syntax is:
 use database_name;

 mysql> use mydatabase;
 Reading table information for completion of table and column names
 You can turn off this feature to get a quicker startup with -A

 Database changed

Finally run the command line below to perform the search and replace, syntax is:
 update tablename set field = replace(field,'search_for_this','replace_with_this');

 mysql> update table_name set field = replace(field,'(','');
 Query OK, 0 rows affected (0.08 sec)
 Rows matched: 450 Changed: 387 Warnings: 0

When completed, exit mysql

 mysql> exit

Let's say you have a database named address_book with a table named contact_list and a field name phone_number.  Some of your phone numbers were entered as (areacode) number and you wish to remove the () from areacode.  Here is what you would do:

[root@e-smith /root]# mysql

Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 2 to server version: 3.23.32

Type 'help;' or '\h' for help. Type '\c' to clear the buffer

mysql> use address_book;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed

mysql> update contact_list set phone_number = replace(phone_number,'(','');
Query OK, 0 rows affected (0.08 sec)
Rows matched: 450 Changed: 387 Warnings: 0

mysql> update contact_list set phone_number = replace(phone_number,')','');
Query OK, 0 rows affected (0.08 sec)
Rows matched: 450 Changed: 387 Warnings: 0

mysql> exit