Hi, our house is a 2-story in MA.
The attic is above the 2nd floor and is 700 sf.
There is a jalousie window at each end. 4 ft tall and 2 ft wide. They are hard to turn, but were open as much as I could get them (probably halfway) over the summer.
For the winter, should I close them a bit, or leave them open?
If that's the only source of venting your attic, leave them open as much as possible.
Read through the link posted by GBR in WA and come next year you can explore the better options of roof ventilation that will both improve your comfort level in the summer months and mechanical protection from snow build up & ice damming in the winter months.