Hotmail provides users with option of changing the themes. This can be done using the Options menu available as part of Hotmail Account.
Login to your Hotmail Account
Click the Options link available on the right hand side and select More options from the available menu list.
Under Customize Your mail section, click the choose a theme link.
You can pick any one of the standard themes as the desired theme for your hotmail account.
If you want to change theme as the time and weather change in your location then you can go for Dynamic Themes. You can enter or search for the location.
After selecting your desired standard or dynamic themes, click the Save button to Save the changes done to the themes.