I can't install it because simply when I run the installation in no way I can delete any partition.
As far as I read it cannot be removed, because it is integrated in the tablet, however I have no space to put win10 on the system partition. Any advice ?
You have to boot from windows installation media (not running windows setup from within windows).
Then you can format old windows partition and install windows 10 into it.
With 32GB of storage space you'll soon run out of space. Then it becomes a nightmare for managing free space.
Windows 10 can't normally operate for a long period with so little space.
120GB is bare minimum for comfortable use, 240GB is recommended.
I'd suggest, you reconsider your wish to migrate to windows 10.