Go to Android Settings > Location & Security > Device Administrators > uncheck SeekDroid if it exists. Now navigate to Android Settings > Applications > Manage applications > All Tab > SeekDroid > and Click Uninstall. After it is finishes uninstalling you can reinstall it from wherever you purchased it. Now you can reopen SeekDroid from the app drawer and log into your account.
You may notice you have the same device on your account as twice. The bottom one is the one that was just added, so you may remove the top copy by clicking the trash can.