Update manual.md

docs/manual.md

@@ -15,7 +15,7 @@ The purpose of this software is to automatically locate and carry-out high-throu
 		3. *https://sites.imagej.net/FlyReg*
 		> To add each URL you need to press [Add Update site] and in the line appeared on the bottom of the table type the corresponding URL in the **URL** column.
 		> The updated Update sites table should look like this:
-		> ![alt text](images_for_manual/manage-update-sites.png "Title text")
+		> ![alt text](images_for_manual/manage-update-sites.PNG "Title text")
 		
 	4. Close *Manage update sites* dialog
 	5. Click *Apply changes* and wait until new dependencies are downloaded