The current contract will still keep the CZK currency that you had at the moment of signing it. So, the currency will not change.
The currency will change to EUR only with the renewal accommodation agreement and only in case your apartment has a preassigned currency of EUR.
Can it happen next year the currency of my apartment might change to EUR?
Yes, actually in the next two years all apartments will be offered only in EUR. At this moment there is only a part of apartments in EUR and another part in CZK, but in the future all apartments will be offered only in EUR.