Hi there! What do you mean by changing format?
Do you want to resize a design?

You'll need to have software or a machine that can resize for you. You are wanting to change a rectangle to a square, and the results of that do not usually come out well. It gets distorted and squished looking. If you just want to make the design smaller so that it fits inside a 4x4 hoop, in your software you'll need to just change the 7 to a 4, and not change the ratio.

When making a design smaller in my software, ARTSIZER--free, it also lowers the stitch count. This keeps the density appropriate to the size.
Format refers to design names, different formats for different machines. .ART and EXP for my Bernina. There are many others, PES, HUS, etc.
Hope this helps. If you need more help use Inbox on top of page and type small letters sandyqueen and your message. I will know when I have a PM by a red number by Inbox.

SQ

You can resize a design in embroidery software, and there are free version to do that. But beware, too great a reduction might cause problems as small details become very tiny. You can reduce a 5x5 design to a 4x4 without too much trouble, from 5x7 to 2.8 x 4 might be too much. So you have to test before you sew it on a project - always a good advice but when resizing a must!
And when testing you might consider using same sized cotton squares so you can make a patchwork project from all sort of tests.

I wouldn't resize a design that much. For many years (until I bought a new machine with much larger hoops) I have reduced the size of many designs by 10% because they were a bit too large for my hoop and that 10% sometimes was too much because the fill had been changed and not for the better. You are talking about reducing from 7" to 4" and I would not recommend it at all. Maybe somebody else can advise you better.
Welcome to Cute Embroidery. Hugs, Lidia