Google unveiled changes to its mobile-payment system Wednesday in a bid to get the upper hand in the battle for control of consumers' "digital wallets." The revamp allows a consumer to load any existing credit- or debit-card number into a software application, which then can be used to make purchases using smartphones equipped with a special computer chip.

Google Inc. GOOG +0.66% unveiled changes to its mobile-payment system Wednesday in a bid to get the upper hand in the battle for control of consumers' "digital wallets."

The revamp allows a consumer to load any existing credit- or debit-card number into a software application, which then can be used to make purchases using smartphones equipped with a special computer chip. The changes aim to eliminate barriers to enrolling in the service.

The move comes as payment networks Visa Inc. V +0.64% and MasterCard Inc.,MA +0.05% wireless carriers, and other technology companies like eBay Inc.'sEBAY +1.25% PayPal are rolling out numerous systems aimed at turning consumers' smartphones into virtual credit cards.

Google Wallet, despite being one of the first mobile-payment services to become commercially available, has seen limited adoption because of competition and technical hurdles, such as requiring partnerships with banks.

When Google Wallet became available in the fall, consumers could make payments using a Google-branded prepaid account that was preloaded into the app or load the app with certain MasterCard-branded credit cards issued by Citigroup Inc., C -1.23%its first and only bank partner to date.