Hi Michael

A couple of things:

When using the button in the WYSIWYG editor to add an image to the content then yes there is a bit long list of existing image assets, but you should be able to scroll down to get to the Or add a new Image section of the form. Is this not working? Are you unable to scroll? If so can you let me know what device or browser you're using, as it seems to work fine for me when I try it!

If you you go to the Content > Assets Library section of the admin pages of your site then you can tidy up the existing list of images. You can delete them if you want to, but first make sure you aren't using the image anywhere on the site. Alternatively you can create folders and move images into them. This helps keep things organised rather than having everything in one big list!

Thanks

Joe