Set your homepage to BT Yahoo in the options menu of your web browser. Copy the web address for BT Yahoo into the box that allows you to designate a homepage and save the changes. Close out of your web browser and restart. BT Yahoo will then appear.
The options menu is found in slightly different locations depending on the web browser being used. In Internet Explorer, it can be found in the Tools menu located at the top of the browser window. In Google Chrome, it can be found by clicking the wrench icon. In Firefox, it is accessed by clicking the orange Firefox button in the top left corner of the browser.