First steps into AE : need to change video lenghts on template

Hi

I bought with my sub Clean Corporate Showcase / Presentation by RomanP on Envato Elements
Well Im totally new to AE and still all went fine, but video clips are too short, theres like 10 place holders with 1 video of 5 sec each, but I need to make it 10 sec long but I dont know how.

If there was a button to double whole video lenght would be fine.

Any clue how to do ? THanks