what is the difference between grany & grandma they both have the same meaning but is there any difference??

Question

Answer

Here in the US "grandma"  (pronounced "gramma") is much more common.  People might use "granny" in a funny / joking way.  I think it's more common in the Southern and Western parts of the US.

A famous "granny" from American comedy show was this lady:
http://www.colettebaronreid.com/blog/featured/beverly-hillbillies-4th-chakra/comment-page-1/

Answer

No difference whatsoever.
BTW "granny" (two n's)

Answer

Granny and grandma are shortened forms of the word  Grandmother. Other English names used for grandmother are Nan and Nanna. 
Example: Tomorrow I will visit my granny/grandma/nan/nanna.