The retailer, part of the House of Fraser group, will be rebranded under the House of Fraser name after the facelift, which starts in the autumn and is expected to take up to three years.
New escalators and air conditioning will be installed in the shop, which was once a powerful performer on London's most best-known shopping thoroughfare but in recent years has started looking decidedly down at heel.
House of Fraser, which also owns Dickens & Jones and Army & Navy, said it wanted to make the DH Evans premises as upmarket as its Barkers store in Kensington, which was given a pounds 6m makeover last year.
The company said it was changing the name because it felt the DH Evans brand did not have the same loyalty as some of its other stores such as Dickens & Jones on Regent Street. "Our experience of other name changes is that it is not a big deal for shoppers," said John Coleman, House of Fraser's chief executive.
DH Evans was opened by Welshman Dan Harries Evans on Oxford Street in the last century. It was quickly expanded but Mr Evans died penniless in 1928 after a series of unsuccessful property deals.
House of Fraser is also planning to spend pounds 14m on its Army & Navy outlet in Guildford, Surrey, which will also be rebranded under the House of Fraser banner. It will close for six months next year before re-opening in September.
The changes have been made possible by a pounds 172m property deal struck yesterday by House of Fraser. It has agreed to sell the freehold of 15 of its outlets to property group British Land. It will then lease each of the stores back over a period of 40 years.