You have a couple of options for rotating elements:
Offline editors or advanced online editor
Manual Rotation:
When you select an element, a small blue ball (or two arrows in a ball shape) appears above it. You can click and drag this blue ball with your mouse to freely rotate the object to any angle.
Exact/Snap Rotation:
Go to the Object Menu > Rotate.
Here you can rotate exactly 90 degrees clockwise or counterclockwise.
For a custom angle, you can select "free rotation," which pops up a window where you can type in the exact number of degrees you want it to tilt (this option is available for the offline software only).
Instant editor and App:
You can rotate exactly 90 degrees clockwise or counterclockwise through the Edit image menu.