Note: Once you have changed the text it may not be centered on the image anymore. So I'm going to show you how to do that too!
How to Edit Text:
I'm going to show you using the Spice Labels. The real trick to this is that the text is part of a grouped object and must be "Ungrouped"
1. Make sure that the Select Arrow is highlighted in the tool bar. (It is by default.)
2. Click on one of the circles to select it. Adjustment lines will show around the object that is selected.
3. Go to the Object Menu and select Ungroup. Or hit Ctrl+U. This will split the object into 3 pieces. 2 circles and 1 text object.
4. Click on the white part (to deselect all of the objects) or go to Edit->Deselect All.
5. Click on the text in the circle you ungrouped to select it. Then double click on it to edit it. A green border will show around it.
6. Change the text as desired. Lastly, click on the white background to Deselect the text.
Now you've changed your text! But it might not be centered anymore. Follow the directions below to center it.
How to Align a Group of Objects:
There are several options for aligning a group of objects to each other. With the spice labels, I want each object centered on the one below it.
1. Select all the objects to be centered on each other either by holding Ctrl and clicking on each item, or by right clicking the mouse and dragging it over the items to be grouped. (Just make sure you don't get any of the nearby objects when you do this.)
2. Go to Object->Align->Align Center-Middle (which is the same as choosing Align Center, then Align Middle). You can do the same in the Align Options Window (on the right side) by selecting Centralize.
*If you're not familiar with the Options Windows on the right - Align is the one with 3 different size rectangles adjoined by a line in-between. You can also get there from the Object Menu by going to Align->Show Align Options...
3. Lastly, while you have all the Objects selected, regroup them by hitting Ctrl+G or going to Object->Group
I hope that helps you start finding your way around a little better in Silhouette Studio. With a little bit of practice, you'll be able to get the hang of it.