Having 2 alternative local area connectios

Hello!
Let me try to describe my issue in my non-professional way, as I am not very strong with the technical part of connecting to the internet.
I have home 2 internet connections. Sometimes the first is slow and the other is fast, on other times the second is slow but the first is fast, so I need to switch between these 2 connections.

First came someone from the first company. He installed the connection and connected my laptop to the internet. For this connection he used on my computer a "local area connection", which is connected using "Broadcom NetLink (TM) Gigabit Ethernet". On the internet protocol version 4 properties screen he checked the option of "Use the following IP address" and "Use the following IP address", and entered the relevant ip and dns values.

Second came someone from the second company. To install the second internet connection, he used the same "local area connection", and just modified the selections and details on the internet protocol version 4 properties (here the is obtained automatically) and the dns values are different.

How can I switch now back to the first connection? And then if I want to switch back to the second connection? Do I have to modify the internet protocol version 4 properties each time? I am a little worried about doing that each time again, I am not a technical expert and I am not sure if I can do it right...

Is there a way, instead of modifying the internet protocol version 4 properties each time, to create an second local area connection on my computer so it would only need to click on the right connection every time i want to switch a connection?

Thank u!

You can add both subnets to your TCP/IP advanced properties window which should allow you to choose one or the other. You click the "add" button then add info like DNS,IP,subnet,default gateways from both connections to the list.

Thanks for answering. Great, seems like there is a way!
When I go to the advanced TCP/IP setting on my computer, I see it a little bit differently than on your screenshot.
Under "IP Addresses" setting it says: "DHCP Enabled", and the "add" button is disabled. What is that? How can I enable the button?