Unfortunately, the size can not be changed in the desired way. You can change the size of the icons in the taskbar but only for a very limited number, 3 sizes : small, medium(default) and large, using the registry. Here it is how :
1. Open Regedit. You can do by hitting Windows key + R and typing regedit or by searching for regedit, using the search menu.
2. Navigate to HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced.
3. Create a new DWORD (32-bit) Value by right clicking in the right window pane and selecting New->DWORD (32-bit) Value.
4. Name the value TaskbarSi.
5. Set the value to one of the following to 0, 1 or 2 which give you small, medium or large. You set the value by double clicking on TaskbarSi.
6. Close Regedit and reboot.
You will now have the size of taskbar icons you set. If you don't like it, you can always go back and change it.
or
you can use the attached registry teak files