I have a new light I'd like to install in my dining area. The lights wire is not long enough to hang from the ceiling to end up where I'd like it. How do I extend the existing wiring or remove the existing and replace the wire? Thanks for any help.
Unless it happens to be end of line you will have three cables. Feed to lamp, Feed from lamp to next, and Switch wires. As a result not too easy to move extending is really best option.
Simple option is to just extend the flex. Normally a simple lamp does not have an earth but as soon as you replace for a fancy light then an earth is required unlike all the other wires in the ceiling rose the earth is normally a clamping screw where as the rest are in terminal block built into the rose.
First there is power at a ceiling rose even when the switch is off so isolate at the consumer unit before working on it. In the projects section there are some pictures worth looking at. The return from the switch should be marked with red sleeve or tape is twin red has not been used. But often this is not the case. If you decide to remove the ceiling rose make sure this wire is identified first. Normally you have two wires (Brown and Red latter often a black with tape or sleeve on it.) Then three wires all red, Then three wires black black Blue. I am using old colours if very new house blacks become blue and reds become brown. The red (or black with sleeve) with the brown only two terminals in block is one to make sure it is marked. If the sleeve falls off and it gets mixed up with other two blacks it is hard to locate again. And connecting all blacks together if this happens will blow fuse so be careful. Often if you need to extend it is easier to change flex to three core and hide original box in ceiling and use second box where new light is to be. Unless it is end of line which means only two cables in ceiling rose. Anyway look at projects page a lot easier to understand a drawing than following written instructions.
The flex has the feed and return hooked under lugs in rose so normally the earth cable needs to be a little longer and the feed and return only just long enough so no cores are seem once lid is replaced on rose.