I have the same problem on the Dyson V10 Animal. I was afraid to apply too much pressure on the red tab, which needs to be pushed in the forward direction to open the canister.

I did not want to risk breaking the transparent clip at the bottom of the canister with a screwdriver as recommended above.

I found once I had opened it, I observed that the red clip locks onto an outpouched area on the main device (See picture with green arrow).

I found that the red clip will click forward if I apply pressure simultaneously on the grey column below the red clip (See picture with red arrow)

Hope this helps.