Go to NadekoBot\src\NadekoBot and backup your credentials.json file; then go to NadekoBot\src\NadekoBot\bin\Release\netcoreapp1.0 and backup your data folder.
Follow the Windows Guide and install the latest version of NadekoBot.
Paste your credentials.json file into the C:\Program Files\NadekoBot\system folder.
Paste your data folder into C:\Program Files\NadekoBot\system folder.
If it asks you to overwrite files, it is fine to do so.
Next launch your new Nadeko as the guide describes, if it is not already running.
If you are running Dockerised Nadeko
Shutdown your existing container docker stop nadeko.
Move you credentials and other files to another folder.
Delete your container docker rm nadeko.
Create a new container docker create --name=nadeko -v /nadeko/:/root/nadeko uirel/nadeko:1.4.
Start the container docker start nadeko wait for it to complain about lacking credentials.
Stop the container docker stop nadeko open the nadeko folder and replace the credentials, database and other files with your copies.
Restart the container docker start nadeko.
If you have NadekoBot 1.x on Linux or macOS
Backup the NadekoBot.db from NadekoBot/src/NadekoBot/bin/Release/netcoreapp1.0/data
Backup the credentials.json from NadekoBot/src/NadekoBot/
For MacOS Users Only: download and install the latest version of .NET Core SDK
Next, use the command cd ~ && wget -N https://github.com/Kwoth/NadekoBot-BashScript/raw/1.4/linuxAIO.sh && bash linuxAIO.sh
For Ubuntu, Debian and CentOS Users Only: use the option 4. Auto-Install Prerequisites to install the latest version of .NET Core SDK.
Use option 1. Download NadekoBot to update your NadekoBot to 1.4.x.