Component upgrade

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How hard is it to upgrade the rear derailleur, front derailleur and shifters? Not planning on changing out the crank.

I have SRAM SX5 for a RD, generic Shimano for a FD and SRAM SX4 for shifters. I would like to upgrade all of these to SRAM X.9.

Can I just change these components out or is it more difficult than that?

Thanks,

Rob