Doubling the size of an image

1. When you double the size of the existing image, there will be jaggy lines obvious. You can't drastically remove them, but can reduce and blur a bit to soften it.
2. Image > Image Size.
3. Double (or adjust at any ratio) the existing value of the width. The height will be proportionally increased with respect to the width and the ratio of increment. Or vice versa.
4. Filter > Noise > Despeckle to reduce the jaggy lines.
5. Try to Blur a little bit (like 0.2) to reduce more jaggy lines.
6. Filter > Sharpen > Unsharp Mask. I used Amount = 50% for this example.
7. For this example, the result is not drastic. The bigger the drawing and the size, the more effect you get. The picture on the right should look clearer than the middle one :(