Just go to the step with the image you want to replace and click the Replace Image icon. Here is what will happen:

1. ScreenSteps will have remembered the exact size and location of the original capture on your monitor and will open a capture regions with those dimensions. You can reposition or resize the capture window based on your needs.
2. After you hit return to capture the image the image will be replaced in your lesson. But the annotations (arrows, boxes, ovals, etc.) will not replaced. You can just reposition you annotations on the updated screenshot.

You never have to redraw all of your annotations from scratch. This will save you literally hours when updating a large manual.