Lithuania joined the Eurozone in January 2015, trading in its litas for the euro.
ATMs are ubiquitous in cities and towns, and even the smallest hamlet is likely to have at least one. The majority accept Visa and MasterCard. Change money at banks, though the easiest way to carry money is in the form of a debit card, and withdraw cash as needed from an ATM.
Visa and MasterCard are widely accepted for goods and services. The only place you may experience a problem is at a very small establishment or for a very small transaction. American Express cards are typically accepted at larger hotels and restaurants, though they are not as widely recognised as other cards.