You may prefer to use the NextGEN galler – see post here
If you find you do not have the correct level of access to carry out this task, please contact synergy support.
How to make an image gallery/slidehow…
STEP 1: locate the image files you wish to use in a gallery
STEP 2: Sign in and begin editing the post to which you wish to add the gallery
STEP 3: Click to upload/insert media
STEP 4: Drag and drop the image files you located in STEP 1 to the Drop files here area
STEP 5: Wait while upload completes
STEP 6: DO NOT insert media into your post, instead simply close the Add Media panel.
STEP 7: decide where you would like the gallery/slideshow browser to appear in your post, and type the following short code there:[[portfolio_slideshow]]
the gallery/slidehow will not be shown in the editing area, but will appear on your post. You click to save as a draft, you can click to preview and you will see the gallery, or of course, you may publish, and then click to view the page.
TIP: If you wish to modify details (e.g. captions etc) of media you have uploaded, sign in, and select Media > Library from the dashboard. You can edit details form here.