I have just recently downloaded a few games which I remember playing from 15 years ago. I have noticed that the resolution of the games seem much less than I remember. Is it just me or is this true. Any way to change to the original resolution quality.

You probably have a bigger monitor than you did 15 years ago. :) 320x240 looks pretty spiffy on a 12".

CGA and EGA only supported the one resolution, and VGA supported two (but the higher res at only 16 colours).

Change the DosBox config file to run in fullscreen and mark the "fullfixed" as True. The there are two parameters for DB to resize the width and height of the screen.