Textures like that usually come in binary sets of numbers i.e. they usually stick to numbers like 64, 128, 256, 512, 1024, etc. See if any of those textures come in sizes similar to those numbers. If they do, consider stepping them up one level i.e. changing a resolution from 128 X 64 to 256 X 128. Another thing to keep in mind is maintaining the proportion between width and height in a texture. If you're going to increase the size of a texture, make sure you adjust both the width and the height so that they have the same proportion as the original texture. Finally, needless to say, back up your work. It would be killer to mess up a texture and then misplace the original.
Hope this helps!