Hopefully someone will chime in with an official site answer, but if not, and depending on how faithful you need it to be, you could always use Waifu2x:

https://waifu2x.udp.jp/

to enlarge the image 4x (to 1400) and then resize it to 750 in another program (waifu doesn't have the ability to set more specific target ratios, so far as I know, but doing it like this would probably get you a clearer image than using another program to do the enlarging in the first place).