The drop shadows on applications in the Windows 10 preview are really big and suspiciously similar to the ones in OS X, and if they aren’t your speed, you can easily remove them. We actually think they look good, but since somebody out there won’t like them, here is how to disable them.
Open up Control Panel and head to System and Security and then System, and click the Advanced system settings link.
Alternatively you can use the Start Menu and search for “advanced system settings” and click on that item.
From here, go to the Advanced tab and click the Settings button under Performance.
Find and uncheck “Show shadows under windows” and click Apply or OK.
The drop shadows will immediately be removed.