Can you change the channels from the buttons on the TV?
Are you using the internal tuner of the TV or a cable box or satellite receiver?
What type box do you have ?
Is it cable? or Satellite? Which one?
Can you change channels from the buttons on the cable or satellite box?
If you have extended cable and you are not getting all of the channels then you have a problem with the cable box or it's programming. The number of channels is controlled by the cable box not the TV. The tv is used only a a display device for the cable box.
There are two possibilities on why the remote won't change the channels.
1. The remote may be bad or have a bad keypad which will let some functions work but not others.
2. The cable box has lost it's programming or is set for basic reception only
( this should be resolved by you local cable company, they will usually
replace the box)
If the channels will change from the buttons on the cable box then I would
suspect the remote.