How do you delete old channels and enter new ones on a cobra sr900 scanner?

There's no need to delete existing programming. Enter a new frequency on a channel and it will replace the existing one. T program the scanner,

Power Up

Press manual

Press 1, manual to go to channel 1

To program 155.250 in to channel 1

Press 1, 5, 5, .(decimal), 2, 5, E/enter

Press manual to advance to the next channel, repeat above for each channel and frequency

Press scan to scan the programmed channels