How do I safely switch all my data from Nokia 520 to 920?

Switching to Nokia 920 from 520 (which is already running 8.1). I need to upgrade 920 to WIN 8.1.

When do I put my ATT SIM card in, before or after I upgrade?

When I remove SIM card from 520 can I put it back in without losing any thing?

Thanks.

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