There are various ways by which you can launch disk cleanup in Windows Technical Preview.
In the Search box type in Cleanmgr.exe and press the Enter Key.
Via Run Menu:
Press W+R keys to launch Run menu.
In the blank space type in Cleanmgr.exe and press the Enter Key.
Create a Pin to Start or Pin to taskbar:
Open Control Panel\All Control Panel Items\Administrative Tools
Locate Disk Cleanup
Right click on it to opt Pin to Start or Pin to taskbar option.