How exactly do you downgrade Tekkit Classic to a older version ((the version before the newest))

[Xicoman10]

Update, Because I have a server and cba to update it for the update, And my friend has a new launcher so I downloaded it and can't find the way to downgrade it, I have a old technic launcher and I can easily downgrade it on that, So anyone know how to do it ?

[Richs_Yard]

Well first, update the launcher to the newest version, and then select your modpack of choice, and then press the gear and select the build.