How Install Windows 7 x64 in UEFI from Legacy Win10,Ubuntu.

Hello,
I made this thread asking for your help.
Actually i have on my computer (orginally windows 10 in uefi when i bought) but now installed Kubuntu 15.4 OS and Windows 10 OS x64 in Legacy Mode,
on HDD 2TB (MBR).
I drop Grub bootmanager, writing in windows 10 recovery mode console commands
" bootrec.exe /fixmbr " and " bootrec.exe /fixboot "
so when i turn on my PC, only Windows 10 shows up.
(Its good because now i can safety delete Kubuntu without problems with booting).

Now im asking you for help, its question.
How should i install windows 7 x64 in UEFI Mode step by step?
I have right now Bootable USB with Windows 7 x64 type MBR (UEFI and Legacy bootable) FAT32.

Because i have only key for windows 7 x64 ultimate
there is a way to check key from windows 10 already installed
but other install windows 10 have new key so old will dont work.
I can of course ask from shop for key (received system at bought computer)but i can't contact them,
tried everything so in my opinion install again windows 7 x64 ultimate and update to windows 10 its good idea, only left problem with convert bios from Legacy to UEFI

So should i first uninstall linux, then reverse from windows 10 to windows 7, then i can with any errors (show me now when i try boot usb in uefi these windows 7 on actually installed linux and windows 10 on hard drive and i receive communicat:
file:\windows\system32\winload.efi error code: 0xc0000001
for try just execute screen of installation windows 7 i tried boot pendrive in legacy mode then i receive another communicat:
with no right's to read harddisk at loading installation screen. "not exacly said, just describe")

run installation of windows 7 x64 from boot uefi usb, clear all harddisk and install new system in uefi (windows 7 x64) and uprgrade him to actually system windows 10 then change secure boot to uefi mode ?