How can I reload .spacemacs file after editing without restart emacs?

I found the solution: SPC f e R

It is from "Dotfile Configuration" in the Spacemacs Docs.

SPC q r or (restart-emacs-resume-layouts) will restart emacs whilst preserving the layout.

For those who work in emacs mode, it might be little difficult to get this done with keybindings. In such case, do M-X then type dotspacemacs/sync-configuration-layers

SPC f e R doesn't work for me so I personally use SPC q R. It completely restarts spacemacs though - but if you maintain sessions (dotspacemacs-auto-resume-layouts t) in config), spacemacs will restart with same buffers. Hope it'll help someone.

dotspacemacs-auto-resume-layouts is a config option which can be found in setq-default section of your .spacemacs file. It comes with default spacemacs setup, it's default value is nil.