Why and when?
Long ago people believed it was essential to repot yearly. Nowadays, repotting is not essential for the plants to grow since you feed them regularly. Succulents, cacti and epiphytes (such as orchids) seldom need repotting because most of them live in crevices not having enough room.
Nevertheless, we do repot plants, every 3 to 4 years. Repotting should occur at the beginning of the growing season (end March for most plants) or at the very end (end of September for most plants).
First, before repotting get a pot one side bigger from the original pot. Do not jump into three to four sizes bigger because this causes the plant to make extra unneeded roots.
Second, make sure the plant that needs repotting, its soil be on the dry side. Prepare the second pot, put a layer of crushed clay pots at the very bottom of the pot. Fill 1/3 of the new pot with the compost you are using, and set aside.
Third, tap lightly on the edges of the pot while holding the main plant with the other hand. If there are any roots coming out through the bottom holes of the pot, cut them with clean scissors. Now remove the plant with its soil without breaking it apart. Remove the decayed and dead roots if any. Check if the roots are pot bound, if so, try to untangle a little the mess work of the roots, allowing them to grow in the new pot. If the root ball is too dense cut a little bit from the tips. This being a good stimulus to allow the roots to regrow in the right direction.
Forth, now water the plant thoroughly (you can overwater, since it’s the first-time watering), this will allow the air from the soil to escape, in the form of bubbles.