Loosen the nut on the threaded rod that goes through the spring. The nut is for adjusting the tension of the spring. Loosen or remove the nut completely and you should be able to easily open and close the hinge. IOW, release the spring tension first. This also makes re-attaching the hinge a snap. Re-tension the spring after you remount the hinges. Adjust to the desired level of tension to offset the weight of the lid so it stays open when lifted. You may need a deep socket to do this as there usually won't be much room inside the hinge leg to use any other type of wrench.