You can change youre username en password in advanced setting. Change it and try it, when you change it upload youre website again to youre server.

in advanced setting you see you name, username and password maybe you write youre name and not youre username? 

Hi Stefan & Der Zwoemti, it's not working. When I type http://www.mywebsite.com/admin into my address bar, another website is loaded, which is http://website.1and1.com/#top Why is this? And even if I enter my username and password in this unfamiliar site (from Advanced Settings -> Access Management), it says wrong username and password.

Where did "www.mywebsite.com" go?

Anthon

what is your domain name?

did you register www.mywebsite.com? who is the registrar?

who is your host company?

My host company is GoDaddy. The site www.mywebsite.com is not mine. It's supposed to be the site I have to enter in order to access my Control Panel, according to Website X5's user manual.

Unless there's a mistake somewhere...