Hi de jean, and welcome to the Forum! Firstly, you need to make some space for GNU/Linux - a word of warning though, I did manage to install GNU/Linux alongside Windows 10 but on a rig that did NOT have an EFI enabled BIOS.
This is what I had with Windows 10 partition wise on a 200 Gb drive:
1. 350 Mb System Reserved partition
2. 186 Gb System partition (C:\ drive of Win10)
3. 450 Mb Win 10 diagnostic/recovery partition
First is to shrink your C:\ drive using Windows own 'Disk Tools' - Computer | System Tools | Disk Manager - highlight the main C:\ Partition and right-click for a context menu and select 'shrink volume' - allow Windows to do this automatically.
Second, after you have created the space run chkdsk, then defrag before proceeding.
Third, boot into your Zorin DVD in 'live' mode and select the 'install to hard drive' icon on the desktop - when the choice comes up, select 'other method' rather than 'auto'. Create an 'Extended partition' in the space left after shrinking Windows 10 and then create the following partitions:
1. 512 Mb '/boot' partition formatted to 'ext4'
2. 30724 Mb '/' (system) formatted to 'ext4'
3. At END of extended partition, make 'swap area' of 4096 Mb
4. What is left between '/' and 'swap area', format to 'ext4' and mark as '/home'
5. Make sure that you direct GRUB to be placed in your '/boot' partition.
Back in Windows 10, install EasyBCD - on first run this will automatically back up your current mbr so that you can always go back to a working Windows 10 if things should go wrong - which they shouldn't. You need to add the GNU/Linux entry into the mbr by pointing to where GRUB2 is as that is what is used by Zorin.which you placed in - '/boot' so it should be easy enough to find by the size of the partition.
Other considerations are:
1. Turn off the 'advanced power settings' in Windows 10 which merely puts the hard drive to sleep - otherwise you will never be able to boot into Zorin.
2. Turn off 'Fast Boot' in the BIOS.
Hope this helps!
