If you do not have Photoshop, try this. You may well be infringing someones copyright by doing it unless it is your own film.
If you use Windows 10 (or Windows eight) you can type 'Snip' into the cortana search and start the snipping tool. Run your film and pause it at the frame you want, watch that you are not between frames. Follow the instructions in the tool to save the frame to your clipboard or a hard drive location. Paste it into a photo editor. The Quality can only be as good as the original quality of the film.
Sony A7, A850, A77, A700 || Sony>> 70-300G, 28-75 f2.8 SAM, 16-80CZ, 50 f1.4, FE 28-70 OSS, FE 24-70CZ f4 OSS, LA-EA4 || Minolta>> 300 f4 G HS, 200 f2.8 G HS, 100 f2.8 (D) Macro, 50 f1.7, 28 f2.8, 28-135 f4-4.5, 70-210 f4, 500 f8 Reflex, TC x 1.4 HS, TC x 2 HS. || Sigma 21-35 f3.5-4.2. || Tamron SP 24-135.