Ok those tabs are not it...you have to get to the cru, to do that you have to first remove the top duct assembly it has a screw just under it, it should be visible once you hit the button which releases the canister, but the screw can not be accessed until you detach the top duct assembly which is held in place by two clips left and right of the duct's base front. Hit the button the duct will pop up, and by pinching the front of the base of the duct pressure on those clips will release it, you can now get to the screw. I Have to review the schematic again but either the two other screws become accessible at this point from the top and the unit will release giving you access to the power switch, or you have to remove the post filter and two more screws become accessible from the bottom. Let me know if you understand so far and I'll have a closer look at the schematic...but this is what tricked me up. It's all very easy if you come in from the top, I tackled it from the bottom up and ended up tearing down the cru, and it did not need to happen...
Ok it releases from the top once the top duct assembly is removed, I believe it's three screws that become available at that point and it frees the cru there is another large clip to the rear of the post filter, I believe that has to be released as well in order for the unit to come free, and "then pressure applied to the two white visible clips" help release it as well, it's simple and straight forward from that point...I remember kicking myself after realizing the simplicity, but dyson is notorious for the hidden clips... let me know if this helps, I'll try to walk you through it if need be...I am working on another vacuum at the moment and trying to recall all the details of the dc39 a bit hazy...maybe time to do a tear down and reassemble video...? But it was very straight forward once you find the hidden clips...