How to modify duration?

I created a slideshow but without slideshow generator. I put 78 pictures on the timeline. Duration is automatically set to 3 seconds for all pictures. I tried to modify the duration for all the pictures but it is not possible. If I right click on a picture I Can see the duration of the picture but the value Can 't be modified. I Guess I have to delete all pictures to the timeline and do it again with the desired value ?
Thank you by advance.

You can manually change each of the 78 image clips on the timeline,
remove the track and use the slideshow generator, or
start the project over and add the images using a new default image duration.
To change the default duration of an image, you most open one, anyone, in the Source player, change Properties > Duration and then click Set Default.
Shotcut does not provide a direct numerical control for the duration of any timeline clip, but you can use the seek actions/shortcuts as seen in the Player menu and snapping to the playhead to adjust a timeline clip to a certain duration.

Hello @shotcut,
Thank you for your explanations. Slideshow generator is very useful…