Press 'Enter' on the keyboard, and then type in 'i'mcheater' and then press enter again. This lets you type in the other cheat codes.

Press enter and type:

Destroy selected object'byebye'
Full map'eagleeye'
Damage enemy buildings'ups'
Get indicated amount of money'moneymoneymoney' <number>
Destroy everything 'hastalavistababy'
All units healed 'strongman'
All enemies destroyed'gotohell'
All enemies destroyed; only works once 'blitzkrieg'