To remove lens block, you have to push the 2 metal rods from one side to the other. The rods have one end thinner than the other

Now you can remove every lens in order to clean them from dust or humidity

When re-assembling, there's only one way to get them back in, so keep track of lenses order and direction when removing each one of them. Or wou'll have to try many times to comlete the puzzle.