Open the image in Photoshop Elements and flatten any layers: Layer>Flatten Image.
Resize the image:
Use Image>Resize>Image Size and ensure that the Resize is (bicubic) and Constrain Proportions and Resample boxes are ticked. Then, under Pixel Dimensions type 1400 into the width or 1050 into the height box, whichever is showing the larger number of pixels. The other number will automatically adjust accordingly.
Click OK to complete the process.
Use Image>Mode>RGB Color to convert the image to RGB if it was prepared in Grayscale or Indexed colour.
Use Image>Convert Colour Profile>Convert to sRGB Profile.
Use File>Save As to save the image to disk or pen drive. Remember to rename it – Short Title followed by underscore (_) then your name e.g. The Tree_John Smith. If you are using a Mac, include the jpg extension as appropriate. Format is jpeg maximum quality.