There is a simple way to change the size of Windows 10/8/7 Taskbar Thumbnails. If you find them to be a little too small for your liking, go ahead and make them bigger!
Increase Taskbar Thumbnail Preview size
Open Regedit & navigate to the following location:
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Taskband
In the right-hand panel, create a DWORD value named MinThumbSizePx.
Right-click MinThumbSizePx and select Modify. Set its decimal value to say, 300.
Exit the Registry Editor & Logoff > Logon.
You will now see that the taskbar thumbnail size has increased.
We all know how to increase thumbnail size in Windows Vista, but if that method does not work, then you may try this method which has been by my MVP colleague Ramesh Srinivasan.
UPDATE: Our Taskbar Thumbnail Tweaker may interest you.
