At first, you must know how the frame and the lenses are combined together. Then use the cleaning cloth to grasp the lens to avoid smudging and fingerprints and then start to remove the lenses from the frame. Put your lenses in a right place. Next, find the exact place to seat the lens first. Then install your lenses which should be grasped with a cleaning cloth. At last, you can try them on to see whether they are comfortable to wear. If they are not, you can adjust the glasses by yourself little by little.
It is not easy to replace the frame. I have tried once but it failed. You can hardly find the same size of frame as your original one. So , you had better leave the task to the professionals. Take time to find an experienced optometrist in your city.