Summarize this article:

Use the following steps to download the Photo Resizer app.   Open your Android's Google Play Store. Tap the search bar. Type in photo resizer hd. Tap Photo Resizer HD. Tap INSTALL. Tap ACCEPT. Wait for the app to install. Tap OPEN in the Google Play Store, or tap the Photo Resizer HD icon on your home screen. It has a blue icon with four arrows pointing in. It's in the middle of the screen. This will open your Photo Gallery app. It will open in the Photo Resizer HD app. This is the Resize icon. This icon opens the resize menu. It's at the top of the menu. Alternatively, you can tap one of the image dimensions in the list to quickly resize the image. There are two text fields for the horizontal and vertical dimensions. You can use either to edit the photo size. Tap the text field and then type the number you want for the image size. For example, if the text field has "300" written in it, you would replace it with "150" to halve the image's file size. You cloud also replace it with "600" to double the file size. Check that the checkbox next to "Keep aspect ratio" is checked to ensure that the image size stays proportional as you resize the image. It's at the bottom of the menu. This will apply your changes to the photo. This floppy disk-shaped icon is in the top-right corner of the screen. This saves the photo to your Android's Photo Gallery using your new dimensions.

Summary:
Download the free Photo Resizer HD app from the Google Play Store . Open Photo Resizer HD. Tap Gallery. Tap the photo that you want to resize. Tap the icon with a diagonal arrow. Tap Custom. Type a new image size number in the text field. Tap OK. Tap the icon that resembles a floppy disk.