Abbey Spectrum 620/5 corner marker lights

A quick question.

How do i change the bulbs?

It's not mentioned in the manual. 

Obviously i need to remove the lens but i dont wanna do it wrong (using brut force) and break it.

At the bottom of the lens i can see a little cut out but i can't see a screw inside it. I guess it just prizes off but it seems a little reluctanat to play ball and i don't wanna break it.

Thamnks in asdvance

Si'