Hello i am using ATmega328pu and i am running out of SRAM. I cannot change anything else on my code. I am thinking using ATmega644p but i am not sure if i have to change the libraries that i use(TinyGPS+, Altsoftserial, SDfat, CC1101).

Any help would be great.

The ATMEGA1284P is around the same price, twice the flash, four times the SRAM.

I have used it with a wide variety of libraries, inlcuding TinyGPS, SD - no problems so far.