Hi @Dharanidhar Malladi!

If they are already different sizes, I think the easiest way is to put them next to each other and drag the  ones you want to change, aligning them with a single frame of reference using the alignment lines that shows up whenever you put objects or frames in close proximity.

If you are creating the frames from scratch, I suggest using the aspect ratio presets, or creating a custom frame. The next frame you create will then be the exact same size as the last created.