Download IMGBURN

Now all that’s left is to glue the iso back together. In ImgBurn this accomplished by:
Mode -> Build
In the ‘Source’ section, click the ‘Browse for a folder’ icon. Select c:\iso\ms-iso.
In the ‘Destination’ section, click the ‘Browse for a file’ icon. Give your iso a name and put it where you’d like.
Under the Options tab on the right, set ‘File System’ to ‘UDF’ and ensure that ‘Recurse Subdirectories’ is checked.
Under the Labels tab, set an appropriate label (eg., ‘win2012-virtio’) in the UDF field.
Under the Advanced -> Bootable Disc tab:
Check the ‘Make Image Bootable’ checkbox
Emulation Type: None (Custom)
Boot Image: c:\iso\ms-iso\boot\
Platform ID: 80×86
Developer ID: Microsoft Corporation
Load Segment: 07C0
Sectors to Load: 8 (for Vista and earlier, this would be 4)
Patch Information Table: Unchecked
Finally, click the ‘Build Image’ button on the bottom left