Once the barrel is freed, the rest of the assembly comes apart once the pieces are rotated - they are 'nested' within helical tracks inside each 'shell'

Before you disassemble it, note carefully how each 'layer' is nested within the next one. Otherwise it will take a lot of trial-and-error to put it back.

The focussing ring assembly also 'drops out'. To re-assembleit, align the 3 tabs in the barrel with the slots in the inner helicoid (inner part of the focussing ring), then turn it 45º.

During re-assembly, ensure that: 1. the ribbon cable doesn't get snagged. 2. the white focusing gear needs to sit into the black pillar (highlighted in step 4)

Useful document: Parts Catalog for Canon EF 35-80mm III Lens