Question About Bonds

For all the experts out there:
got a question about bonds...my parent bought me 30 yrs bonds from 1991-1998. Earliest one matures in 2021. I checked the value of all of them from 1991-1994 and the value is more than face value...about 40% avg and collecting 4% int rate. The last ones from 1995-1998 are a few $ more than face value now collecting 1.66% int rate. Do I cash them out? What should I do? I was thinking of cashing out the 1.66% int bearing ones from the late 90's and holding on to the ones from the early 90's collecting 4% until they mature.