Change pictures

i would like to change a pictures in Explorer template
i try to change it for my host but this make a error and all site stop
i try again by adding them to the Images in template but they not showing in site

there any way to add them without this problems
can i add it for the source template files before upload it and how
if not how after i upload it
what the size of this images
i use 1800*515PXL and 300 resolution

Thanks
Husam

Which images are you referring?

the main 6 images in header1

You go to Module manager in joomla admin, find module named "Hot Full Carousel" and click on it. Go to options tab, there you will find slide1 - slide20 slots you can configure