On my V8, I used a small screwdriver to lever back the spring clip at the bottom of the bin, then opened the bin door. This spring clip is designed to work like this and you will not damage anything..
This enabled me to empty the dust out and look at it in detail. There are two small cross-headed screws fixing the bin to the bottom of the battery case, and on my V8 these were a little loose after 3 years of use and there was movement between the bin and the battery frame
There are two Torx headed screws holding the top end of the bin with a bracket, removing these and the bin came off with its red release lever. Remove any accumulation of dirt & dust under the lever.
The top of the cyclone chamber was then pulled off and behind it about half way down the handle is the spring latch which locks the bin in place. . Mine looked ok so after cleaning I slotted the cyclone chamber back in and tested the release lever. Without the bin it worked perfectly, so I decided that the 2 loose screws mentioned above were not clamping the dust bin tightly enough.
After reassembly the bib release handle worked fine again, though as one contributor mentioned, a little WD40 or Silicone spray will make the opening work more smoothly until a coating of fine dust builds up to lubricate the movement.