Put on gloves before you begin. The fire bush is not irritating to the skin, but gloves will protect your hands from sharp branches.
Trim your fire bush in early spring, before the plant blooms, using garden shears. Cut around the plant to shape it to the size you want. Work symmetrically around the plant, stopping frequently to step back and check the progress of the trimming. In most cases, trim back only enough to maintain the shape of the bush or to keep it from encroaching on walkways or other planted areas.
Cut the bush more extensively if frost has damaged it, by removing as many of the damaged branches as possible. This allows new, healthy growth to occur.
Clean up the area and dispose of the cuttings and branches.