Okay so i suck at explaining things but I'm going to try my best here.
First, Ты will open both of these pictures:
Set their size proportions to 533x300. [Make sure Ты have the option to 'Constrain Proportions' selected - this way when Ты put in your width, 533, it will automatically make the height the correct size, 300.]
Next step - now that Ты have both Обои resized, open a new canvas/blank background & set it's size to 265x265
Drag both Обои to the new canvas - At this point your new canvas should look like this: