1. Launch GIMP and click on the "File" heading. Select the "Open" option from the "File" menu to load your GIF file into GIMP.
2. Click the "Open the Layers Dialog" tab in the floating "Layers" window (see Tips). Each of your GIF's frames will be displayed in the "Layers" window, with the duration of each frame displayed in parentheses. You'll need to increase the display speed of each frame to slow down the entire animation sequence.
3. Right-click on the first frame, then select the "Edit Layer Attributes" option from the pop-up menu that appears. The selected frame's name and duration will appear in the "Layer Attributes" menu's "Layer Name" field.
4. Edit the value inside of the parentheses, in the "Layer Name" field, to specify a higher display time for the selected frame. Click "OK."
5. Edit the duration of the rest of your GIF's frames by visiting the "Layer Attributes" for each frame. Right-click on a frame, then click "Edit Layer Attributes." You can also opt to edit a group of frames if you only want to slow down a portion of your GIF.
6. Click on GIMP's "File" heading, then select the "Save" option to store your GIF's changes.
May this helps you !!