How to update LyX 1.5.3 to 1.5.5 or higher

[Waluyo Adi Siswanto]

I am using LyX 1.5.3 under Ubuntu(ME).
How can I update to version 1.5.5 or higher, I could not find the update
in Synaptic package manager. Is there any command that do the update
directly to the LyX site.

Could anyone help me..