The main split
The generally established procedure — with profit tax and value added tax. The special regimes — under article 18 of the Tax Code these are turnover tax, and also the special taxation procedures for participants in production sharing agreements, for participants in special economic zones and for certain territories.
What the choice depends on
The annual income (the threshold for turnover tax is one billion so'm); the type of activity (for example, turnover tax does not apply to imports, to the production of excisable goods or to audit activity); the demands of your counterparties — VAT payers often prefer to work with a VAT payer.
Changing the regime
You change the regime in the order and within the time limits the law sets. Under article 462 of the Tax Code, a legal entity moves to turnover tax from the next tax period, and informs the tax body at least ten days before that period starts. If the total income passes one billion so'm, the move to VAT and profit tax is mandatory from that day.
Advice
Make the calculation at the start of the year: if the growth of your turnover leads to a change of regime, plan for it in advance.