How to Enable / Disable Recent Files List in Windows 7 Taskbar Jump List

First to edit the number of files shown in that list:

1. Right Click in your start menu and chose Properties
2. Click on Customize button under Start Menu tab
3. You'll get the Customize Start Menu dialog, at the bottom of which you will see the Start menu size section where you can set a new value for Number of recent items to display in Jump Lists
3. Set your preferred value and click on OK twice to apply the settings

Note that setting Number of recent items to display to 0 will remove the recent files list from taskbar, but still store your recent files at the back-end. So that you can restore it later.

To completely disable this feature:

1. Right Click in your start menu and chose Properties
2. Under Privacy section, You can find Store and display recently opened items in the Start Menu and the Taskbar check box. Uncheck it.
3. Click on OK to apply the settings.

Hope it helped!