I have many small scanned pictures. How do I increase their size avoiding focus problrms?
Are you talking about small photos that you want to scan and increase their size for printing or displaying on a computer? If so, you need to scan them at a very high resolution.
If you have already scanned the photos and now want to increase their size without affecting quality, that can be problematic. There are a number of new plug-ins that allow you to do this. But, there is not much in Elements that will help you "sharpen" a low resolution photo when it is magnified.
If you can give us more specifics about your problem, we may be able to offer more help.
Focus is not affected by scaling up. But the result is usually terrible. This is like trying to turn chicken soup back into chicken...