Okay, here's the situation. You have a low to mid-range steel string acoustic or electro-acoustic guitar with a non-adjustable bridge. The bridge is made of an insert of curved plastic. You find that the strings are too high for comfort, and that holding bar chords, for example, is very tiring.
What you can do, fairly easily and quickly, is to modify the bridge to provide a lower action. This is an irreversible modification, short of buying or making a new bridge, so make sure you're not just wimping out of developing strength. Also make sure the fault isn't in the neck - ensure that the neck is reasonably straight. I take no responsibility for any damage caused by following this suggestion - you are on your own!
What I did was this: find a guitar that you find easy to play and want to copy. Make sure the difference isn't all in the string gauge: if not, measure the distance from the bottom of each string to the top surface of the 12th fret on this guitar. Measure these gaps on your guitar - you should find the gap is larger by a couple of millimetres on yours. Note this difference (xn) for each string.
As the 12th fret should be positioned exactly halfway along the string (see my writeup in power chord), we can use similar triangles to see that we need to lower the point where each string touches the bridge by 2xn.
Using a knife, make a small nick in the bridge to indicate the point where each string touches. Remove all the strings and slide the bridge out, making sure you know which is the neck side. Make a mark at 2xn below each contact point. Using a small round file, gently file a dip into the bridge vertically down from each contact point to each depth mark. If you want to be cautious, don't go all the way down first time. You must ensure that the lowest point in the filed out section is vertically below the original string contact point to retain the string spacing. Round off the edges of the dip such that the string will touch the centre of the bridge.
Replace the bridge (right way around!), re-string, tune up and try it out!