Can I swap a SIM card back and forth in an iPhone 5S?

Hiya, i'm clueless at anything related to phones and SIM cards.
Me and my sister currently share a iPhone 5S (until we can afford another phone), we both value our privacy therefore we want different phone numbers. If I bought a SIM card could we swap it in and out of the phone? Would it delete any data from one SIM card? And will a SIM card change the number? Also if the phone is on a contact Vodafone tariff would I need a SIM card from Vodafone?

You can swap SIMS under two conditions: both phones are unlocked, or both phones are with the same carrier. If there's just one phone (like in your situation), the SIM controls it. If YOUR SIM card is in the phone, it will only ring if someone calls YOUR phone number.

The SIM card bears your phone number. Example for two phones: If you put your SIM card from your phone into Phone B, Phone B will ring when someone calls your number.

SIM cards have a small amount of memory, normally used to store contacts, but that's about it.

You would not be able to have different phone numbers -- it's part of the SIM card.