If you can get the specs of the current PC it would help. Mainly processor, amount of RAM, video card. Dell/Alienware makes their stuff purposely hard to upgrade, but sometimes it is possible, especially if it's just lacking in one area or another.
It depends what he plays too - I have a 1080ti which is a 6 year old card, but can power through even the most intensive games, including some VR stuff. Also the monitor being played on - is it 1080p, 1440p, 4k?