How to change the quality of the video while editing in Windows Live Movie Maker

Hey there, I have been using Windows Live Movie Maker for a long time now, and each time I use it, it freezes and lags very often. This happens especially when I add a new clip in, or when I'm simply just trying to preview my movie. The quality of my videos are very good while editing, but it comes at a cost since editing them is a big problem. Being patient doesn't really work because it happens so often. I remember one time, when I added a clip (that I already processed before) into the movie, it gave me a popup that suggested to lower the quality of the clip so that WMM would run more smoothly. I did, and even though the quality was slightly lower, I noticed that there was no lag or freezing at all! It was extremely easy and fast to complete my movie and upload it, and on youtube the quality was still perfectly fine like all my other videos. I'm just wondering, is there any way for me to change the quality of my movie while I am editing it, so that it won't freeze up? (I am not talking about resolution, by the way)