Pretty much any garage door installation or garage door services company worth its salt will offer full assessment, delivery, removal and installation services to its customers. It stands to reason- after all, garage doors are massive pieces of equipment, heavy and pretty complex. Almost everyone investing in a new garage door will allow the company to do the installation.
But if you're confident in your own construction and physics abilities, you can save some money by doing the installation yourself. Sectional garage doors in particular require quite a bit of effort- a simple lift-up door is slightly easier.
In general, you should never try to fix, adjust, or remove your standard torsion spring garage door by yourself. The amount of tension contained within these springs can be dangerous for a single person. Call in the professionals.
But some models lend themselves to adjustment by the lay person. If you're not sure which variety you have, you probably don't know enough to be messing about with them anyway. And if you can't make heads or tails of the instructions that the manufacturer provides, again, you likely shouldn't be making the attempt. Garage doors can be quite dangerous- more so than any other appliance in your home.