Date change on photos

I just got a new iphone with plenty of storage, now my old phone didn't have much storage but i had a lot of photos i liked so i transferred them to my laptop (normal laptop not mac) via dropbox and stored them in my pictures app.

Now when i try to get them to go back onto my phone through the iCloud website any .png photos (Screenshots) won't transfer on, so i figured i'll go one by one and transfer them over to .jpg just so i can have them. I don't mind doing that work.

BUT

one thing i'm really OCD about is them being in the right date and place i took or received them and whenever i put them on it comes up as the last photo being taken or received so it goes to the bottom of my pile. I have tried changing the date on my laptop to the date it was taken saving it and then transferring it and getting the same problem. I have tried changing the date on my iPhone, also same problem. Tried it on both. Also the same problem.

If anyone knows how to fix this so all my photos are in chronological order please let me know because its driving me insane.

Thank you guys.