ATT Sim in the UK.......and marshmallow

Hi All ive got the s6 active from att here in the uk, ive also got hold of an ATT sim which needs activating.
Can anyone tell me if when i activate the sim from the uk i'll be able to upgrade to Marshmallow from 5.02 (baseband g890aucu2aof4) over wifi?

cheers for any answers!

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