Yes you can but theres no point; both Windows 7 and Windows 8.1 will be eligible for a free upgrade to Windows 10 in May/June. Its therefore pointless to spend money on an additional Widnwos license for only 3 months or so of use.
Can I add Windows 8.1 to my XPS 8300 ? It has Windows 7 Premium
Changing Operating Systems from Windows 7 to 8.1 on a XPS 8300