Valentina,
Try this:
1. Open youir image file
2. Duplicate the Background layer, shut off the visibility of the background layer by clicking on the eye icon in the Layers panel, and work on the Background copy layer.
3. Activate the Magic Wand tool in the tool box, and on the tool's option bar set the tolerance to 25 . This tool makes selections based on color. With the Magic Wand active, left click somewhere on the t-shirt and hit delete on the keyboard. Continue doing this until you have deleted the t-shirt. If the tool fetches too much, reduce the tolerance. Leave the hair alone. If there are any littly bits of shirt left, use the eraser tool to get rid of same.
4 Set your foreground color chip to the desired color for replacement - I used red for demonstration
5 .Open a blank layer between the the Background layer & the Background copy layer
6. Go to Edit>Fill layer>Foreground color
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