There are an awful lot of jobs around the house that a homeowner is fully capable of doing. Some of them are painting, putting in landscaping, and possibly fixing a leaking faucet. That being said, no novice should attempt anything other than very basic glass repairs on their own.
There are so many things that can go wrong that they are almost too numerous to mention, but we will discuss a few of them. First, glass is an inherently dangerous material to work with that requires special tools if you are moving a piece that is much larger than a breadbox.
Second, just because you were able to get the old window out of its frame and the new one in without cutting yourself, does not mean that it is not going to leak sometime in the future. Replacing a window is a skill that takes many years of experience to master that absolutely must be done right the first time.
Third, in almost every instance when an old window has to be replaced and it was in a frame, the old material that was used to hold the glass in place needs to be dug out before the installation process can begin. Being able to perform that task not only requires special tools and a great deal of skill, also under no circumstances can the frame be damage because then you will have a real problem that can be very expensive to repair.
Forth, in certain situations the glass will need to be cut so that it conforms to an oddly shape window frame, and that is not a job that most homeowners could perform under the best of conditions. Please do yourself and your wallet a favor, which is the next time you need glass repairs done, hire a specialist that is trained to do the job correctly.