How can I edit the featured image? Usually I upload the image in media, there is one option which says "use as a featured image". This works fine but the output image is badly cropped. I want to know how can I manually crop it (150 x 150) and use that a featured image?
You can add image sizes and cropping settings with the add_image_size() function. Call the declared name of your size at the frontend and you'll have your desired size and crop.
The image is stored as an id, you can pick whatever size you want with the the_post_thumbnail() function. PE: the_post_thumbnail('medium'); will show the featured image with medium settings.
Open your Admin Panel & then first go to Settings > Media. There the first 3 settings allow you to set the different sizes manually. Themes & plugins can override the settings but sometimes they don't.
Then go to Media > Add New
Click Select files & upload your image. You'll see that your uploaded image & some options regarding the title, caption, edit image etc.
Click on edit image, then you'll see many options including scaling, rotating, flipping, cropping the image. There you can edit the main image, it's different sizes as well as thumbnail.
The best way is to upload a sample image & experiment with the options first. Click save when you're done. If you make a mistake, click cancel & start over.