Most of the changes would likely not have materially affected the outcome of the war itself. What would change is that FDR would have bargained hard for specific Soviet concessions or actions in order to provide help or get his approval for the postwar settlement. Some of the below would require an earlier POD, or would be best if done earlier than 1943.
1) Return of all Americans currently living in the Soviet Union in order to receive Lend Lease. That would have enabled those Americans who emigrated to the USSR during the Depression to escape back to the US, including those sent to the gulags, which would have provided a lot of other information about the nature of the USSR. Certainly other concessions could probably be agreed to at this time such as restoration of the independent Baltics, agreement on the eastern border of Poland, and complete repudiation of Molotov-Ribbentropp.
2) The Allies don't simply turn over the Russian POWs back to Stalin because he asked. They either do not agree to it at all, unless the POWs request it, or get Stalin to make concessions on other issues.
3) The US and UK work completely with the Polish government-in-exile to secure an independent Poland. That means the Poles don't announce the Warsaw Rising on their own, but coordinate it with the Western Allies to insure airborne supply drops and Polish paratroopers. The Allies might also insist that Stalin coordinate his attacks in Poland with this in mind, asking for a specific commitment that his troops/tanks punch through to Warsaw once the operation begins.
4) In Spring 1945, emphasis is made on Patton's troops getting as far east into Czechoslovakia as possible.
5) Allies do not agree to supply Tito exclusively over the Chetniks. Instead, they supply the Chetniks alone or at least send them the bulk of supplies.
6) Since Bulgaria never declared war on the Soviet Union, but only the US and UK under duress by Hitler, the US insists the Soviets do not send their troops into Bulgaria. Instead, the US and UK will arrange for Bulgaria to enter into the Allied side and support the Red Army offensive in the Balkans. In essence, Bulgaria becomes part of the Western sphere of influence as the northern flank of British backed Greece.
7) When discussing the nature of free and fair elections at Yalta, specific commitments are made on what ministries will not have Communist ministers. In particular, the Interior/Police ministries need to be kept out of their hands.