Crack the case, look for the flyback transformer and there should be two knobs on it. One is labeled SCREEN (bottom dial) and one is labeled FOCUS (top dial). It should be mounted on a solid black or solid white rectangular piece of plastic right in front of the flyback (black or white large cylandar with the thick red wire coming out of it going to the tube.)
First take a dark pencil or even nail polish and dab a dot on the edge of the control and the plastic surround it to mark your starting point and let it dry. (In case you totally mess up and can't figure out where to return to if you want to get back to square 1)
Then, with the monitor ON, and a long flat screwdriver, carefully turn the focus dial to see if you can make the image any sharper. Do not touch ANY metal part of the monitor, just the plastic knob.
As you turn it should "bloom" the letters either horizontally or vertically, then get sharp, then bloom them the other direction. Find the dead center spot where it is best in focus.
If that helps, great-- you solved the problem. There however is a high likelyhood that this will NOT fix the problem and there are other bad components on the board that need replacing such as capacitors, the flyback transformer or even the tube (in other words, not worth the effort on a $5 PC monitor)
Yes, people strive for slightly-out-of-focus images out of their PC monitors to make it more like the arcade experience.. You got to skip that step... too bad it went too far for high resolution text.
You might want to try a front end that uses LARGE text like the ones designed for arcade monitors and resolutions of 280x240 instead of 1280x1024 like this one is meant for!. You might like the resulting image.