If you find the fixed retainer uncomfortable, have difficulty cleaning around it, or have problems with your gums or tooth decay, the type of retainer can be changed. A lot depends on the problem you were treated for. For example, if you had gaps between your teeth before orthodontic treatment, a fixed retainer is strongly recommended at the end. If such a retainer does need to be removed, discuss with your orthodontist whether a short fixed wire could be left bonded to the teeth that are most likely to drift apart – for example, the two front incisors if you had a diastema. If your only problem was crooked teeth, switching from a fixed to a removable retainer is not a problem.
This answer is for general information. Your own case needs an examination by an orthodontist.