Bulgaria is one of the few European Union member states that still uses its own currency – the Bulgarian LEV (BGN). The Bulgarian lev has a fixed exchange rate for the EUR with a currency rate of 1 EUR = 1.95 lv.
You cal always go to a bank to do an exchange but they will need to register your ID/passport and it will usually take a bit more time. Instead you can go to a Change bureau but you need to have a few things in mind. When going to a Change bureau almost make sure to check the exchange rates in advance and look for a sign with NO COMMISSION.
Avoid changing money on the airport and in hotels because you will not get the best rate.
A few checked and trusted change bureaus in Sofia you can find here:
Make sure you always have a bit of cash along as small shops and restaurants may still not be equipped with a terminal. The same applies to any kind of street shops and small bakeries.
Before leaving Bulgaria also make sure to change all your money back into EUR or dollars to avoid losing it. Coins as usual get much lower exchange rate so make sure to get rid of them.
Here is a photo with some Bulgarian bank notes currently in circulation