You need to have phpMyAdmin installed.

If you do, you go to your database by clicking it's name on the left.

You'll see it's tables listed and right under it, there's a textfield named

Run SQL query/queries on database 'database name'

This is the field where you drop the text (querries)

INSERT INTO setting (settingid, settinggroupid, title, varname, value, description, optioncode, displayorder) VALUES ('', '6', 'Posts to change username', 'postuserchange', '50', 'Number of posts required for the user to change their own username within the user control panel. If you wish anyone to be able to change username set to 0.', '', '18')

INSERT INTO setting (settingid, settinggroupid, title, varname, value, description, optioncode, displayorder) VALUES ('', '6', 'Days between user change', 'dayuserchange', '7', 'Number of days between each time a user is allowed to change their nickname. If you wish the user to be able to change username at any time set to 0.', '', '19')

and run them by pressing GO

You can run both INSERT's mentioned at the same time, or one after another.

However, since you are obviously not familiar with phpMyAdmin, make sure you backup your database before messing with it!

-Alex