If you just want to basically wipe the OS and start again with a fresh out of box experience (OOBE) of windows 10 then I would do the following
BIOS Changes (not essential but I would do this personally at my organisation)
- Make sure it is running in UEFI mode if it supports it (it should be under Boot)
Before you do this
- Backup any files from the laptop as these will be wiped
- Ensure you have a valid Windows 10 licence key
- Go to https://www.microsoft.com/en-gb/software-download/windows10 and download the tool to create a windows 10 boot key or upgrade the OS (I would start again with a fresh OS)
- Once the software is downloaded put your USB Stick into your device (Make sure its at least 8GB) and go through the necessary steps (Choosing language, x32 or x64) I personally would choose x64 if your device has more than 4GB of RAM.
- When prompted choose the option Create installation media for another PC
- Choose USB Flash Drive and then this will create a bootable USB stick to install this
- Plug the USB into the device you want to install Windows 10 onto and turn the device off
- When powering this on, if it is a Lenovo think pad press the enter key as it boots up, keep pressing until you hear a beep or it produces an option menu on the screen.
- Choose Boot Menu
- Select the USB
- Wait for this to boot to the USB
- Once it boots up choose Install and agree to the EULA
- if prompted for an option of which OS to install, choose the OS that matches your licence (Professional/Home etc)
- If prompted for the licence, enter this.
- When given the option where to install windows choose the disk. If this says Drive 0 unallocated space, then click next. If it doesn't You will need to delete the partitions however.... This will remove everything from the previous windows 7 installation so ensure you back everything up first!!
- Then click apply and wait for the installation
I hope this helps :)