Hey guys,
a lot of you new texture pack makers are wondering, "How can I make my texture pack more HD!"
I have your answer.
It is actually really simple.
You don't need any thing complex like photoshop; you could have something more simpler like paint.net!
Here are the steps:

Image>Resize>Change drop down box to nearest neighbour.

Then in the box you will need to times the number accordingly...

16x16 = Defualt
32x32 = X2
64x64 = X4
128x128 = X8
256x256 = X16
512x512 = X32

PLEASE NOTE:
If you make a texture pack with a high resolution, major FPS drops may occur, it depends on the users computer.

If you are struggling, here is the image tutorial.

Firstly open your photo editing software:

http://i1106.photobucket.com/albums/h369/DynamoGaming/StepOne.png

Then, open the desired image you wish to edit:

http://i1106.photobucket.com/albums/h369/DynamoGaming/StepTwo.png

Click the image button:

http://i1106.photobucket.com/albums/h369/DynamoGaming/StepThree.png

After that, click resize:

http://i1106.photobucket.com/albums/h369/DynamoGaming/StepFour.png

In the drop down box, change it to nearest neighbour or neighbour:

http://i1106.photobucket.com/albums/h369/DynamoGaming/StepFive.png

Then times the number by (?) look at the chart above to find (?):

http://i1106.photobucket.com/albums/h369/DynamoGaming/StepFive-1.png

Click OK then you will be able to edit more pixels and add extra detail!

NOTE:
All the things you will need to edit are in the minecraft jar.
You will need winrar or 7-zip to acess this,
Type in the the bar at the top of my computer or a folder:
%appdata%
The files you can edit are:
achievement
armor
art
enviroment
font
gui
item
misc
mob
terrain
title
pack.png
pack.txt
particles
terrain.png

Copy these into a seperate folder, and your all set to go!

If this helped, show your appreciation by giving me a diamond to help spread the word!

Yours faithfully,
~wilko

Paint.net download:
http://www.getpaint.net/