Here are the steps:
1) Browse to your IP address https://xxx.xxx.xxx.xxx:portnumber and login to webmin with root password. Port number and root� password as per login information emailed to you.
2) At left sidebar, Servers >> MySQL Database Server, look for Change Administration Password at global options.
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3) Enter your new password twice and press Change Now. You are are advised to change to complex password with combination of alphanumeric and symbol.
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That's all.