Hey Baris,
Here's a quick fillet workflow. The thing to note is I do the larger fillets first, then work down to smaller ones. Your original model had some tiny fillets already at the top and bottom..



[EDIT] While I was making the video you made some posts that talked about sizing, and Michael also discussed the "previous fillets" issue too....

Anyway...

ps. At the end of the video I realized I used a "chamfer" on some of the top edges. For the attached model, I backed up and filleted those.