You can not separate flattened layers (they have becomed one layer), only from history to go to step when you have flattened image.
Flatten Image command is in Layer menu Layer > Flatten Image.
One only - however, pre-flattening there could be considerable numbers of layers making up the pictures content
layers are separate images stacked one above another, layers can have transparent areas so you can see content below
If the two pictures have been saved back as anything other than a PSD file which keeps the pictures as layers(seperated) then you cannot just split them off. Basically if the picutre was merged in photoshop (flattened) and saved it loses its ability to be split off
In Photoshop you can easily go back, change what is drawn, recolor drawing, keep elements on separate layers and hide them, delete at any time ...
There are many resources and websites that offer information about Photoshop layers. Some of these websites that offer information are Adobe, Photoshop Essentials and Photoshop Cafe.
Every image contains at list one layer but you can have as many as you want. Layers are separate images which can contain transparent areas or different levels of transparency. People use layers to create compositions in Photoshop because every layer can be edited separately without affecting other layers or composition. Another advantage is because you can save layered image (PSD, PSB, TIFF ) and edit layers at any time you want. Photoshop offers several type of layers like Type layer so you can change typed text only for example. When it comes to save image you can flatten image or to save flattened version of image on disc and leave composition as it is with all layers for further editing at later time. In other words saved layered image serves as template which can be edited even after 10 or 20 years.
Layers are separate images which can contain transparency and can be combined as one single photo. Photoshop offers many kind of layers: blank, type, shape, fill and so on. Layering means you have multiple layers in document and you can manipulate with them: with their position, transparency, also you can group, ungroup them for better organized document and so on.
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It is to make one composite layer from multiple layers. It is like having coffee, milk and sugar separate then you mix them (put them together in cup). Note that you don't have access to change amount of coffee or sugar separate as it is with merged layers.
color layers is simply color layers
Open the Layers window.
The text can be deleted if you have a .psd file with layers intact, simply delete or turn off the type layer. If the file is flattened use the clone tool and cover the type with whatever is behind the text.