How to solve the HTTP Error 500.19 - Internal Server Error on our college website

You can find the web.config file contents as below. I'm told that recently our hosing providers migrated their services to new server and changed all the credentials. On internet i found some solutions to change the user credentials. I really don't know where i can change and how.

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<system.webServer>
    <security>
        <authentication>
            <basicAuthentication enabled="false" />
            <anonymousAuthentication enabled="true" password="[enc:AesProvider:U57nH36GCR0Dt2ylJ3KOHwmpC1Y/8c9M1sNwHwbgIi4h1x6YIfsLuZL9K3eF1wXu:enc]" />
            <windowsAuthentication enabled="false" />
        </authentication>
    </security>
    <directoryBrowse enabled="false" />
    <defaultDocument>
        <files>
            <clear />
            <add value="index.htm" />
            <add value="index.html" />
            <add value="Default.htm" />
            <add value="Default.asp" />
            <add value="Default.aspx" />
        </files>
    </defaultDocument>
</system.webServer>