Boston developer Related Beal has acquired a five-building portfolio in the Financial District from Fidelity Investments with plans to upgrade its office and retail space.

Known as The Block on Congress, the acquisition includes 343,000 square feet of office and retail space at 54, 68 and 282 Devonshire St. and 15 and 19 Congress St. in Post Office Square. Terms were not disclosed.

Related Beal will attempt to revitalize the space, which contains “long-dormant” street-level storefronts, the company said. Renovations to 82 Devonshire St. and 35 Congress St. are planned, with updated office space and 38,000 square feet of new retail storefronts. The work is expected to be completed by early 2015.

“Rarely do you have the opportunity to reposition and reinvent an entire city block, especially one in the heart of downtown Boston,” said Stephen Faber, executive vice president of Related Beal, in a statement.

Related Beal is active in various Boston development projects including the Lovejoy Wharf mixed-use project near North Station. In August, it pulled out of the $1.6-billion planned Quincy Center redevelopment project, in which it had been partnering with developer Street-Works of White Plains, N.Y.

The Block on Congress acquisition is part of the Related Real Estate Recovery Fund, which closed in January 2012 after raising $825 million.

CBRE represented Fidelity in the sale and will handle the retail leasing for Related Beal.