Topfield 5800/Troubleshooting/Delete Channel
Duplicate channels may give bad recordings (if a poor quality duplicate channel is used) and may cause various problems with TAPs. To delete a duplicate, old or unwanted channel, press OK to bring up the Channel List, select the channel, then press the Red button and choose the Delete option (note that you cannot delete channels while recording).
You may also want to rescan to include any new channels, especially if there's been a Freeview reshuffle recently (which may have caused channels to appear to be duplicated).
There are TAPs available which can automate the process of deleting the low quality duplicates or other collections of channels (e.g. pay channels).