No need to upload any clips. I understand now.
Please note that once you put a “frame” (or maybe “still” would be a more apt name?) on the timeline it is not an image anymore and also not an individual frame. Kdenlive converts it into a clip that, by default, will be 5 seconds long, and will contain 5 x the number of frames per second you have set for your project. If the number of frames per second you have chosen is 30, Kdenlive will insert 150 (5 x 30 fps) frames; if 60, 300 frames, etc.
But, to answer your question: for individual clips, right-click (click with the the right button of your mouse) on the clip you want to change and a menu will pop up. Choose Edit duration from that menu and a dialogue will pop up which will allow you to do just that. See image below.
You can use the spinners on the right or click on the numbers an type in the duration you want.
Note that the notation is
hours:minutes:seconds:**frames**
So, if your project uses 30 frames per second and you want 2 and half seconds (instead of 5). You’d do:
00:00:02:15
Because 15 frames is half second of film in your project.
If you have a lot of stills in your project and don’t want to change every one by hand, before putting them on the timeline, got to Settings in the top menu, chose the last options Configure Kdenlive.
In the dialogue that pops up, the first option is Misc, and, at the bottom of the pane on the right, you’ll see a box that let’s you change the duration of image clips, which is what you want.
See below: