Step 1: Downloading the texture pack.
Simply download the texture pack that you want to use.
Step 2: Get a file manager, I use ES File Manager :)
Step 3: Open and extract the pack, as so

Step 4: Go to this directory: sdcard>MineTest

Step 5: Open the folder and locate 'textures'

Step 6: Go back to your downloads folder and copy the extracted pack, then, after you copied it, rename it 'pack' then go back to the MineTest folder, then: MineTest>textures>base, then paste the file in there
Step 7: You should get a screen like this:

Just click Apply To All then overwrite.
Step 8: Open MineTest and enjoy!
