The MetaMorph shop resides in Lambda Mall, right opposite the Main Portal and is the outlet for customizing your avatar as you travel around the Otherland network. Currently the store uses the Credits that you have accumulated.
If you came here from the tutorial, you'll be wondering where all those options are? The MetaMorph pedestal in the tutorial allows you to make some changes to your characters dimensions and energy tints. The one in Lambda Mall has a far wider range of options.
There are many options to make the character look the way you wish. Including size, gender, body style, skin tone, eye colour, hair style and colour, etc.
You can adjust the size of your character within certain limits. Click on the size icon (shown arrowed in the first image below) then use the sliders to adjust the characters dimensions.
Below the sliders are all the other options, use the scrollbar to view them and just click on the ones you want to take a look at. The changes will be immediately applied to the paperdoll image of your character so you can see what they will look like.
When you've made all the adjustments you want, click the Accept button on the left. You'll receive a confirmation dialog telling you the cost of the changes. If you're happy with that, just accept the changes and you're done.