To add your company logo, insert an image using 'Power Tools'. This will come up as the default 'JotForm' one. If you look at properties, you'll see that it points to a web address where the image is stored.
I usually create/find that address by right-clicking on the logo I need and select 'View image in new window'. The address for that page (provided the image appears as you want it to, is the one you should copy and paste into 'Properties' for the image on your jotform.
Check after you do this that the dimensions are correct as the 'insert image' function is set up for the Jotform dimensions and yours may be stretched.
Hope that helps.