How to make high-res .jpg of SW model?

Try the 'Save As' command and select the 'JPEG' option.

If you use the save as JPEG option you won't get a high res jpeg.
Better is to render to a high res with a rendering program. Most versions of SW have photoview 360 built in. Go to the options in PV360 to choose the required image format.

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Like what Hans de Ridder said. Do it on PhotoView 360 and choose the option 1920x1080 and render quality "MAX" save as JPEG