Hi Patty,
You have gotten I believe one of the best programs for ME. It is a very simple program and you should have a Help File along with it.
To change a design size go to tools, from there you can resize to your hoop or by putting in new fields. It depends on the disign just how much you can change it. It will add stitches or remove them but only up to a certain point. A very dense design will not resize smaller very well, on the same token a very light design will look sparse when you enlarge it to much. Just play with it and if you are not sure always do a test sewout.
When you start putting your files in it DO NOT remove them from the hard drive. Also do not change where they are located, the program will not be able to find them and it will tell you 'file not found'. Arrange your files on the hard drive for the catagory you are doing and then put that design in the same catagory in CATX. Example; cats to cats, flowers to flowers etc. I learned to hard way about this. When you have 2500 designs you have to know where they are.
Also make notes about your designs after the sew out, it will help in the furture when you use that design again, you can do this right from the CatX page.
Hope this helps and let us know if you need more help.
Marge