@Karina-Silva - You sure can! Select them all (use Shift + drag to select a group of objects) and then using the context menu, select your size. You can also change the color (and other options) from the context menu:

In the above video, I used the Auto layout to nicely align the stickies after resizing them.

Once they are all the same size, you can also select all and use the white dots on the corners to resize:

So easy!!!! Thank you so much!