I have a number of videos mainly downloaded from youtube. The vast majority have 25.00fps.

I have just purchased a windows 10 laptop and upgraded the windows essentials to the latest version. The videos I have downloaded since have a fps of 29.970 fps. I cannot combine videos with the different fps into a single video.

I am not sure how to get around this. Is there a way of unifying fps, preferably by increasing them all to 29.970 (or better!) If not, is there a way of changing the fps at the time of downloading the videos from youtube? 

Sorry if this all exposes my complete ignorance in these matters!