If you don't have experience installing multiple OSes, I recommend trying it out on an old unused computer first. It's safe as long as you know what you're doing, and it's also very practical. VirtualBox is more for "test driving" operating systems; it isn't ideal if you're using the OS regularly.
I personally recommend dual booting Windows 7 and
Lubuntu. Windows 10 is spyware and serves no benefit aside from DirectX12 and the windows store. Power users will likely switch 100% to GNU/Linux once Windows 7/8.1 security updates and hardware are discontinued.
If you decide to go through with it (Only recommended if you have experience with installing OSes and formatting partitions), then here's a rough outline of what you need to do:
1) Backup all Windows 10 files (Passwords/bookmarks, game saves, list of programs installed, My Documents/Desktop/etc, AppData, software licenses, and anything else important - this is a crucial step and there are tutorials elsewhere on how to do it.)
2) Run the Windows 7 installer (you may need to disable secure boot/UEFI on Windows 8+ machines).
3) Format the hard drive (Make sure everything is backed up since it will be lost!) and create a new partition for Windows 7, leaving free space behind for Linux (Maybe 15-20% of HDD space for Linux? That's up to you.)
4) After Windows 7 is installed, install Lubuntu by creating a new partition using the remaining space (The main parition is '/' and there's also a a swap partition which serves as "backup ram", which is typically set to the amount of ram you have).
Now you can dual boot using the GRUB bootloader, which is part of Linux. Alternatively you can use Windows Boot manager, but it's simpler just to use GRUB. You can configure the Lubuntu panel settings to act similarly to Windows by disabling multiple desktops and rearranging the applets.
