Double hung and single hung windows have more moving parts than other styles of replacement window typically do. Long-term use can cause wear and tear on the different mechanical parts of the window that may cause parts to need to be replaced. A couple of things should be considered before attempting to perform any repairs on the window yourself.
Companies do not want to pay for their customers' mistakes. It is common practice for humans, even a professional, to simply bite off more than he can chew with a particular job. To that end, review your warranty information or contact the manufacturer of the company before doing anything. In most cases, attempting to perform repairs as a non-certified, unauthorized party will void your warranty. It may be irritating to have to wait to get a service professional in; but you will be glad you did if your windows develop serious problems further down the road. The warranty is not an entity to be taken lightly. Understanding what is permissible and what voids the warranty is completely necessary before attempting to replace single hung window parts yourself.
For the sake of argument, we will assume that the warranty is no longer applicable for this job. The next step would be deciding on whether it is a Do-It-Yourself job or if one should employ a professional. Replacing a single part on your single hung window may not seem like a huge job at first; but there may be more to the job than you had originally anticipated. The installation and maintenance of windows is not a duty to be taken lightly. One minor screw up can completely compromise the efficiency of the unit and allow the weather to do damage to the framing. Utilizing a contractor will help protect your windows because you will have recourse if something does go wrong. A licensed and bonded contractor gives you the means to attempt to recoup the costs of a botched job, if it botches. If you do it yourself and make a mistake, then you're just out of that much money and need to pay to repair the damage done. What started out as a small, single hung window part replacement just became a much larger problem.
The best option for acquiring single hung window parts will be through the manufacturer of the window. One may be able to find generic parts to conduct repairs on their windows through a variety of hardware stores or specialty stores. This may not be the best course of action though. If a manufacturer engineers and designs their own hardware, you will likely not get the same kind of performance out of a generic replacement part that you would from the manufacturer's. Of course, this also depends on what exactly you are needing to replace in the single hung window.
It is not feasible to provide an in-depth guide to replacing every part for every make and model of a single hung window. The best way to boil this information down is to contact the manufacturer of the window or check the documentation on your windows. Therein they may list common maintenance or replacement procedures for their product. It should be noted that single hung windows are slowly coming out of style with the growing popularity of double hung windows. Many manufacturers still provide support and parts for their older styles of windows, so you are not just out of luck when a repair situation arises. If you have any doubts about performing the job yourself or it is not covered by a warranty; do yourself a favor and just hire a licensed, bonded contractor. The amount of money you will save from doing it yourself is a pittance compared to how much a faulty repair or bad installation can cost you.