Although you can change your texture pack on both iOS and Android version of Minecraft: Pocket edition, this page is to teach you how to edit your texture packs on Android. The simplest way it to download the app 'PocketTools ' which will allow you to change your skin and texturepack.
To change texture pack:
Download a texture pack for Minecraft: Pocket Edition, for example, Sphax or DokuCraft.
Open up 'PocketTools'
Click 'Install Downloaded Content'
Go to the 'Textures' Tab. This will show the .zip files in your downloads folder. Select your texture pack.
Hold your finger down on the zip, then hit 'Install'
Go back to the main menu.
Hit the 'Tool Kit' button.
Hit 'Change Textures/Skin'
Select Your texture pack and long press that. Hit the 'Use Texture' button. Press the settings button and hit the 'Apply Changes' option. Wait for it to ask to uninstall Minecraft: Pocket Edition, click 'ok'. Then it will prompt to install again. Click 'Install'. Done!
Please note changing your skin will change the skin for all human models, including those in multiplayer (but only look like that to you). The app also installs a new modified version of Minecraft: Pocket Edition so you will need 'Allow Unknown Sources' ticked in your application settings.