The upgrades are the first phase of a fleet-wide assessment of all Carnival passenger vessels prompted by a fire aboard the company's liner Triumph in February, The Miami Herald reported Tuesday.
The loss of electrical power made life miserable for 4,000 passengers and crew for five days before Triumph could be towed to port.
In a statement, Carnival said 10 sailings of Triumph would be canceled, while Carnival Sunshine would have two sailings to Europe canceled.
Triumph is already repairing damage from the fire.
Changes to both ships will include "bolstering" the power capabilities of their emergency generators, the statement said, as well as increasing protection to key electrical systems and electric cables.
Improvements will also be made to systems for fire prevention, detection and suppression.
Triumph is expected to sail again June 3, while Sunshine will return to service May 5.
Cost of the fleet-wide review is estimated at $40 million. Repairs to Triumph, and the loss of revenue in the interim, are expected to be as high as $80 million.
The company's stock price has dropped 12 percent since the fire aboard Triumph.