200 x 200 JPEG images

If I find any albums missing from the Archives I sometimes will add them using the "Add Albums" feature, but when I upload the images for example the album cover, it asks for 200 pixels size and in the format of JPG only, the problem is that when I enlarge or decrese the original size the picture looks a bit too pixely or distorted, how can I resize the Jpeg picture to 200 pixels succesfully, what am I doing wrong?. 

Another tool for resizing images (as well as performing a lot of other image manipulations) is the excellent freeware utility Irfanview (http://www.irfanview.com/) which is also a fast viewer of all sorts of images files and video files. It also plays all sorts of audio files (it can even play OGG Vorbis).