I want to switch to lubuntu 64 bit. Initially i had ubuntu 64 bit. I have saved all the packages in /var/cache/apt/archive; My question is that can I use the same packages for lubuntu 64 bit and install them via synaptic manager?
The packages are the same for Ubuntu, Lubuntu or Xubuntu. The only difference is the default desktop environment. You should respect the distribution versions though, LUbuntu 64 12.04 for Ubuntu 64 12,04 for example.