A door closer on the side door is one of those parts nobody notices until the door slams, sticks, or drifts open in the wind. It is also one of the few jobs in the house where you can often adjust it yourself, test the result, and stop when the door tells you it needs more than a screwdriver. The real question is not whether you are handy. It is whether the problem sits in the adjustment or in the hardware.
Local option: New Plan Care gives families in the St. Louis area in-home help so a parent can stay home: companionship, help with bathing and dressing, meals, and overnight care. Call (314) 405-0887.
Read what the door is doing
Watch the door for a few cycles before touching anything. A door that shuts hard usually needs the closing speed slowed. A door that stops short of the latch may need more closing force or a look at the strike plate. A door that will not hold open at all may have a closer that has lost its hold. A closer that leaks fluid, has a bent arm, or has a loose mounting plate is a hardware problem, not a tuning problem. Name which one you have before you pick up a tool.
What you can adjust yourself
Most surface closers have a speed control on the body, often separated into closing speed and latching speed. Turn the control in small steps and test the door after each change, from the outside and from the inside. Tighten the mounting screws if they have backed out, and check that the arm is straight. If the door still closes too hard after adjustment, or cannot close on its own, the closer may be the wrong size for the door or worn out. Write down what you changed and in which direction, so anyone who comes after you can reverse it.
When the job goes to someone else
Call an installer if the arm is bent, if the closer mounts into a door or frame that is out of square, or if the frame needs shimming before a new unit will sit right. Call them too if the door sits in a frame that needs more than a small adjustment, or if a lock or threshold interferes with the mounting. Ask the installer to show you the old and new closers side by side, confirm the new unit is sized for the door width and weight, and get the warranty terms in writing. Ask whether the closing speed and latching speed will be set to match how Dad actually uses the door.
Test it the way the door is really used
Have Dad open the door from the outside carrying a bag or using his walker, the way he normally goes through it. Watch whether the closer moves the door at a speed a hand can stop without a struggle. Watch whether the latch catches without a shove. A closer set for an empty doorway can behave differently with a load in hand, so the final test should be done that way.
The next move
Tonight, do one thing only. Check the screws and the speed setting on the side door closer, make one small change, and test it three times with the door opening from outside. If the arm is bent or fluid shows on the body, stop there, get a quote from an installer, and ask for the warranty paper in writing before anything is ordered. Local options are listed on the Local Help in St. Louis page.