[Trisquel-users] Re : 13Aug2017 buy Trisquel laptop

[lcerf]

If your disk is (almost) full, you cannot install another system on it.  You  
would need to make space, moving data on another disk. From Trisquel live  
system, you can use the "Disk Usage Analyzer" in the "System Settings" to  
discover what takes most of the disk space.  If you wish, you can move the  
data using the live system too.

https://trisquel.info/en/wiki/install-trisquel-windows-dual-boot-0 details  
the procedure to follow when you do not see the option "Install Trisquel  
Alongside Windows [version]".