Yes you can update the plugin, but make sure that you have taken the previous version banners before uploading.

No problem, Usually you should add the image as banner and it will be available in your media directory or you can get while uploading the banner in newer version. But the banner click url will be added manually. So its better to take click url.

If you would buy, you will get all pro and latest update of random banner. The login details will be send to your after payment

Yes, you can do the remaining payment through your plugin page and then you can download from the login details you have already sent.

Yes, you can verify it in the support page by entering your PayPal transaction ID.

You can add shortcode from version 3.4 onwards,
= In PHP =
echo do_shortcode('[bc_random_banner]');
= Inside the Posts =
[bc_random_banner]
= Options to use in the shortcode =
[bc_random_banner category=category_name slider=no autoplay=true delay=3000 loop=false dots=false]

* category = default / any category
* slider = No / Yes
* autoplay = true / false
* delay = 3000 (in Milli Seconds)
* loop = false / true
* dots = false / true