Your basic resolution is determined by the image scale, which depends on the focal length and pixel size. There isn't much you can do about that except to change equipment.
Stacking multiple exposures will not improve resolution. It will however, reduce noise.
You can make a mosaic, which has several times the number of pixels that a single image does. However, it does not change the image scale or the resolution. Those remain the same as for a single image.
You can use drizzle processing to improve the resolution and image scale. This depends on the data being good enough to support drizzle processing.
Basically, you can't manufacture data that isn't there. If you actually captured high-resolution data, you can bring it out in processing. If you didn't, it just isn't there.