How to change subscriber share path in existing
You should be able to edit the plan using the GUI. Pull up the GUI and select the LogShipping module and select a plan. Press the 'Edit' button'. On the 'Specifiy Backup Options', you should be able to change the shared folder.
Note, make sure any tlog backup or restore processes are complete. To be sure, stop the job prior to making the change. Otherwise, you risk the plan going out of sync.