This is a hard habit to kick. If you are serious about this, seeing an ENT (ear nose throat doctor) is advised. Going cold turkey off of your over-the-counter decongestant spray will get you "unhooked" from the medication after about four to five days. This period will be much easier for you if they get help from your healthcare provider in the form of one of the prescription steroid sprays that can be started about three days before stopping the over-the-counter spray. Sometimes, a brief round (about 6 days) of oral steroids can also be useful.
Quitting yourself is possible also. Some tips are:
1)Quit one nostril at a time.
2)Use oral decongestant pills or syrup during the process for the bounceback congestion you'll get.
3)Use a nonmedical nasal spray as a substitute(such as a saline mist)
4)take up some other bad habit like smoking (ok just seeing if you're paying attention

)
Normal nasal function should resume within 7-21 days.
Good Luck