Under the deal, managing director David Thompson, the youngest of five shareholders when the company was incorporated five years ago, has been appointed chairman.
But directors Barrie Hallett, Ian Ford, Peter Goodfellow and Mike Browning have resigned, the first three remaining as consultants.
Project management specialists Kevin Cooke and Steve Didcott, QS chiefs Mark Stevens and Nigel Maidment, facilities specialist Ian Smith and Birmingham office head Peter Vince become directors.
Thompson said the restructuring was designed to help AYH avoid the problems experienced by many consultants during changes of ownership.
More than 40 staff are being offered the chance to buy into 250-strong firm, and Thompson said he wanted to see increasing liquidity in its shares.
The firm earns £18m in annual fees, and Thompson wants this figure to rise to £25m in the next two years across its UK and Continental operations.
The firm was sold at below market rate, but the price - understood to be £3m-4m, was agreed to be fair.
Thompson declined to comment on the price, but said the firm aimed to gain greater market share in its established markets, and to reinforce its regional and European office networks.
