You will need
- A good reason to cancel a donation, documented.
Keep in mind, the most reliable way to regain presented apartment is "amicable" agreement with the current owner that he voluntarily gave you the right of ownership of the living space. To legalize the transaction will be like a donation contract (i.e. people will give you a flat "back") and a contract of sale. If the current owner to return your former property does not want to, get ready for a difficult court battles.
Examine the current Russian legislation. In particular, in Chapter 9 (paragraph 2) of the civil code contains a list of grounds on which prisoner you once the transaction may be declared invalid. In article 578 of the civil code States the grounds on which you will be able to judicially request the annulment of the contract of donation. If the reasons why you want to return the apartment back, these lists are not included, and if the statutory period of limitations for the cancellation of the contract donation / recognition of the transaction invalid has expired, to start (let alone win) the trial you will be very difficult.
Don't forget that you have a reason to cancel a donation (recognition of the donation contract invalid, the apartment) has to be confirmed by documentary evidence — certificates, acts, protocols, medical reports, witness statements, etc.
Do not regret forces and means, on advice from the specialists. Reasons why you require the return of the apartment and the weight of the collected evidence must to analyze and evaluate a highly qualified lawyer, and not "experts" on projects like "Ответы.Mail.ru". A preliminary consultation with a General assessment of the prospects of the case, of course, can be obtained for free by phone or online on the websites of law firms or in various specialized forums. But if you really want to return the donated apartment, be sure to hire a high level lawyer is a trained professional may be able to find ways to win, even if at first sight it seems hopeless.