Why not just reinstall?
When the pack gets new mods, you need the new version to join. Reinstalling from scratch works, but you lose your keybinds, video settings, server list and map waypoints. This guide keeps all of that.
The short version: import the new pack as a fresh profile, then copy a few personal files over from your old one. It takes about five minutes.
Update the pack
Close Minecraft
Make sure the game is fully closed before you touch any files.
Import the new version
Download the latest pack from the home page. In CurseForge, click Create Custom Profile, then Import, and choose the new zip. Pick All Files when it warns you about files that are not on CurseForge.
Open both folders
In CurseForge, right click your old profile and choose Open Folder. Do the same for the new profile, so you have two windows side by side.
Copy your personal files
Copy the files in the list below from the old folder into the new one. Say yes if Windows asks to replace them.
Launch and check
Start the new profile. Your keybinds, settings and server list should all be there. Join the server to make sure everything works.
Clean up
Once you are happy, you can delete the old profile in CurseForge to free up space.
What to copy
options.txt | All your keybinds, including mod keys, plus video, sound and control settings. The most important one. |
servers.dat | Your multiplayer server list. |
journeymap folder | Your waypoints and the map you have already explored. |
config/voicechat folder | Your microphone, volume and voice chat settings. |
resourcepacks and shaderpacks | Any texture packs or shaders you added yourself. |
screenshots folder | Your screenshots, so they all stay in one place. |
saves folder | Only if you have singleplayer worlds you want to keep. |
Do not copy the mods or config folders (apart from voicechat). The new pack comes with its own updated versions, and copying the old ones can bring back bugs or cause crashes.
If something goes wrong
Kicked with a missing mod or channel message
You are still playing the old version. Make sure you launched the new profile, not the old one.
The game crashes on start
Usually an old file got copied by accident. Re-import the new pack and only copy the files from the list above.
My keybinds did not come back
Check that you copied options.txt into the top level of the new profile folder, next to the mods folder, not inside it.