I do not fully understand the question, but it is always better to produce / export your movie or video in the same format as it originally was in, this results in the least amount of loss in quality. 

To take a guess at what you are asking, when you import a video into movie editor pro plus, you will be notified of the size of the video, and asked whether or not to resize the screen to fit it, I chose yes.

There are other settings in this program to set the default size for your project, click on the letter e on your keyboard, and look under the first tab, which is Movie settings and look towards the bottom of the screen, here you will be able to change the size / resolution frame rate and audio settings for your project,.

 I have only used this program for a few days and am not that knowledgable about it, someone else will hopefully come along and advise you, there is also the user manual that can be accessed via the programs help button, the context help is very good as when you click the question mark and then click it on top of the area you are working in, the approproate help section opens, saves you searching.

Kind regards, john