New Windows 10 Insider preview build 15058 ISOs available for download
An ISO or an Installation media file allows the user to do a clean Installation of windows or to do a manual In-Place upgrade using the official way.
Get the Installation media file before the upgrade for future purposes in Windows 10.
You can download the ISO from the following page:
Download the ISO according to your language and Architecture if you want to do an In-place upgrade-follow the Instructions for making a bootable media on the page itself.