"disminuir paulatinamente" in English

to wane- to work down- to abate- to cut down- to decline- to de-escalate- to drop away- to drop off- to dwindle- to ease- to ease- to ease off- to ebb- to flag- to go down- to let up- to scale down- to shrink- to slacken off- to slacken off- to slacken off- to subside- to tail off- to taper off- to thin- to thin out- to decrease- to diminish- to fall- to lower- to reduce- to cut back on- to lessen- to slacken- to bring down- to cut- to fall off

gradually- little by little