Can the executor of the estate change the will after the som

My grandfather died while I was out of the country so I never got a copy of the will, and wasnt there for the reading. When I came back, I trusted my aunt, (the executor) to be truthful with me. Now, almost a year after my grandfathers death I finally got a copy of the will. The estate hasnt been closed yet, or finalized. I'm not sure what you call it. In the will it states I am the beneficiary. I had no idea, and I know my aunt didnt think Id ever take it upon myself to get a copy of the will. It says that she is to give me money from time to time, until I reach 25. At 25 I am to get half of the remaining balance, and the rest at 30. I contacted my aunt after reading this and now she is trying to say, as the executor she can change the will as she pleases, and they had decided to disburish the money differently. Can she do this?