Free Transform, Image Size, Canvas Size, and Crop tool.
Free Transform
Scale, rotate, skew, and distort the selected layer or selection contents interactively using transform handles.
Select a layer in the Layers panel.
Press Ctrl+T or go to Edit → Free Transform.
Drag the corner handles to scale. Hold Shift to maintain aspect ratio.
Move the cursor outside the bounding box and drag to rotate.
Hold Ctrl and drag a corner for free distortion.
Press Enter to commit, or Escape to cancel.
Transform Options
Action
How
Scale proportionally
Drag corner handle + Shift
Scale from center
Drag corner handle + Alt
Rotate
Drag outside the bounding box
Rotate in 15-degree steps
Hold Shift while rotating
Skew
Drag edge midpoint + Ctrl
Distort
Drag corner + Ctrl
Move pivot point
Drag the center crosshair
Image Size
Resize the entire document (all layers) to new dimensions. Supports resampling with various interpolation methods.
Go to Image → Image Size.
Enter new Width and Height in pixels (or percentage).
Check "Constrain Proportions" to maintain aspect ratio.
Choose a resampling method (Bicubic is recommended for most uses).
Set Resolution (DPI) if needed.
Click OK to resize.
Canvas Size
Change the canvas dimensions without resizing layer content. Use this to add or remove space around the image.
Go to Image → Canvas Size.
Enter the new Width and Height.
Use the Anchor grid to choose where existing content is positioned relative to the new canvas.
Choose the canvas extension color (for Background layers).
Click OK to apply.
Tip:Making the canvas smaller than the content does not delete pixels -- layer data extends beyond the canvas and can be recovered by enlarging the canvas again.
Crop Tool (C)
Interactively crop the document by dragging to define the crop region.
Press C to select the Crop tool.
Click and drag on the canvas to define the crop rectangle.
Drag the edges or corners to adjust the crop area.