I believe you are talking about AirMiles points/miles.
You cannot change existing miles from Dream to Cash
You can go into your preferences and state whether you want newly earned points to go to Cash.
This is socks because the threshold for redeeming Dream miles is absurdly high, so you get stuck with 100's or 1000's of Dream miles you can't redeem. A quick look seems to show the cheapest and least desirable merchandise item costs about 800 Dream miles.
From the AirMiles FAQ
AIR MILES Reward Miles cannot be transferred between your Cash and Dream Accounts. However, you can change your preference as many times as you like.
You can set up or change the balance ratio for your Miles by moving the preference slider from 0% to 100%, towards either your Cash or Dream Accounts. Once set, future Miles will be added to your accounts the way you want. If you change your mind, simply sign back into airmiles.ca and change the preference slider to a different ratio. For more information, or to update your preference, click on the Get Miles
tab and select Set your preference
; or just click here