I have two phone lines in my house and want to remove one. Our main line is in the kitchen, and the alternate is in the office & is hooked up to the DSL. I want to get rid of the alternate line in the office, and change it so that the jack serves our main line & the DSL. There is a splitter already at the office jack for the DSL.

How do I make the wire change at the NID? I can see that there are two screws, one holding red/yellow & a blue wire, the other with green/black & a white wire. I am confused. How do I physically make the change to get back to the one main phone line?

Does anything have to change at the actual jack in the office? I realize that I will have to change my DSL setup with my company to the main phone number, but does anything else need to happen?

I hope this makes sense and really appreciate any help! :)

Take a pic and post using "go advanced/manage attachments"

You will have to put a filter on the phone in the kitchen.

Is the office line a line #1 phone. i.e. you didn't have line 1 and line 2 available everywhere in the house.

But a few tings don't add up with your explanation.

Hmmm... the line in the office is the one we want to change, back to the main number. It is the only one hooked up to the second number.
The kitchen phone doesn't need to change, it already is the main number. I will attach a photo of my NID, currently set up for both lines, but I want to change it just for the main line.

Green/red and black/yellow are the 2 lines. Green and black would go to the same post and red and yellow would go to the same post
If this was a simple L1+L2 hookup.

Something seems fishy because you should have a pair of red/green terminals for two lines.

Here is my NID: https://www.askmehelpdesk.com/landline-phones/nid-box-wiring-145653.html#post691161

The leftmost module is a dud, could be line 2.
The next module is a no electronics module with an auto-jack test jack. It doesn't use the jumper. Those 2 terminals would be the unfiltered line 1. (DSL).

The next module is a whole house splitter. The two terminals on it would be filtered line #1, so filters are not required on each phone.

So here's a pic of the wires in my nid

To be honest I'm illiterate with wiring and just trying to save my parents from paying the $125 to have someone come out. Hope the picture helps.

That shows two phones connected to a single line. One is using the old style wire and the other is using the newer wire.

Remove the modular jumper. Bet you will still have dial tone in the office. There has to be a second location for a phone line. Possibly a cable box. The solid color wiring probably goes to the kitchen.

If this is an overhead drop, see where the wires go.

Is the other line VoIP?

Now, in some ares it is possible to multiplex two lines over two wires, but lets suppose you don't have that. You can look for something inside the house.