Forgotten Router Password

Here is my problem. I was using a Linksys E 2500 wireless Router by Cisco. I thought it went bad, si Go bought me another new router a Linksys E 2500 again because the old was was very good. I installed the new router and set it up worked ok , the problem was my comcast modem not my router. I replaced my modem and then hooked my old linksys router back up and save the new one for later on...