Can alimony which began with my 2000 divorce be modified or eliminated following my retirement?

I am now retired living on a pension of about 48,000 which is much less than I was earning. My salary in 2000 was 56,000, later 100,000 My divorce decree states "plaintiff and defendant have reviewed the other parties' retirement and pension fund statements and waive their respective interests in such accounts and funds." I am 62 and retired due to injuries and physical degeneration sustained over my career. I have had a knee surgery, 2 cataract surgeries and now have impingement syndrome in my left shoulder and maybe rotator cuff damage. In addition a knee operated on in 1991 started to give me problems before retirement and may now need further help. I know the courts frown on retirement before 65 but If I didn't do so, I wouldn't have had enough sick time left to collect my sick bonus which I counted on for my retirement and moving expenses to another state. If I can do this will I incur a heavy expense and can I then arrange to pay it off over time as I am now on a fixed income.