1. Download pspasswd.exe (More info)
2. Create computers.txt file and place it in the same folder as pspasswd.exe
3. In computers.txt list all computers you want to reset admin password. Each in a new line.
4. In command prompt run pspasswd.exe @computers.txt administrator NewAdminPassword
Make sure you have domain admin rights.
All files including a simple .bat script can be downloaded from here.