Can I increase the quality of my photos?
It's not possible to increase the quality of your photos as the resolution of each photo is determined by the camera used to take the photo. As such, there's no process that you can apply to photos you've already taken to improve their quality. It is recommended that you check your camera settings to make sure you are shooting high resolution images to begin with.
If you received photos in an email from another person, or have saved photos from Facebook, it is possible these may be low resolution versions. In this case it might be possible for you to obtain the original photos (which may be higher resolution) from the person who has the images.
Similarly, if you've pre-processed your photos to a smaller size, it would be worth sourcing the original photos directly from the camera.