MyBB Community Forums

As the title states, I recently changed my FTP settings to a new account and get the following error: http://prntscr.com/isqq8j

Which file(s) would I have to edit to fix it?

Its nothing with your FTP settings. Seems like you have changed your database password as well.
Download and open .inc/config.php file in an editor and change new database password in it .
Save the file and reupload (overwrite) to your hosted MyBB directory using FTP.

have you also changed database user account ?
database user details are provided through ~/inc/config.php file

$config['database']['database'] = '_____________';

$config['database']['hostname'] = 'localhost';
$config['database']['username'] = '_____________';
$config['database']['password'] = '_____________';

(edit: delayed response)

Forgive me, but I am quite new to this whole SQL thing. My friend set it up for me and it was fine, but then I got a new FTP user account from my host. I've typed in the FTP credentials, but what would I do now? How would I actually set up the "SQL" thing?

perhaps its better to ask your friend & wait for the help.

or if you have access to your web host control panel then
you may PM me web host panel login credentials to check it.

you (or your friend) can change the login credentials later.