Hi @Viki Sotiriadou ,
You can follow the official Microsoft links below that provide step-by-step details:
Reset or reinstall Windows 10
https://support.microsoft.com/en-us/windows/reset-or-reinstall-windows-10-cd352bd8-4cb6-411a-f2f5-1814bd8d453c
Reinstall Windows 10
https://support.microsoft.com/en-us/windows/reinstall-windows-10-d8369486-3e33-7d9c-dccc-859e2b022fc7
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Best regards,
Leon