(Sorry this was the only up close picture I could find from that time)
I did what you do I went on the internet and I found tons of ideas and solutions to strip that last bit of color from my hair so I could return to blonde. Some were crazy, some were harmful to your hair and some were good and valuable solutions. I am going to share what works and talk about the damage you might do depending on what you choose.
Basically this a a time vs desire thing. The longer you wait and the more gently you let this color fade the better for your already battered hair but the worse and more spotty it will begin to look. I let my hair fade for about three weeks before trying to remove the color and it was already very light however if you colored a darker shade you may be in for a longer wait in order to preserve your hairs health or if you have over toned your hair and it has turned blue or purple you may not care about the consequence you just need to remove the color asap.
First thing I would suggest trying is a clarifying shampoo. People will try to tell you to use dish washing liquid but that is just going to over dry your hair out and it didn't make a noticeable difference to how much hair color was removed verses a regular shampoo also there is no reason to use dish soap when Suave and V05 both make good cheap clarifying shampoos. For me the clarifying shampoo work really well and didn't really dry my hair out too badly.
If you add ground up vitamin C tablets to the shampoo that also really helps and is a trick used in salons to lighten to dark color. You add half shampoo and half powder to make a paste you add to washed, damp hair. Leave this on for at least 30 minutes. Some people have reported that you can use the colored chewable ones but I would test that on a small section first to make sure it wouldn't transfer the color of the tablet to your hair. I did two treatments in a row and suffered no ill effects.
Make sure you are washing with HOT water. Hot showers are the enemy of colored hair and that is why it is recommended that you wash your hair in cold or luke warm water after you have it colored. Doing this, especially leading up to actually trying to the remove the color with help to lighten it significantly.
Color Opps and other hair color removers will help however they are not kind to your hair and especially unkind to bleached hair. They made my hair feel like straw on the one occasion I used it however that was to remove permanent color and I would not recommend it for semi permanent color unless you are desperate and will not be able to go into work or something otherwise. There are also better quality professional products that you can use instead so if you must use color remover go to your local beauty supply store and ask for their recommendation.
Do not try to re-bleach your hair while semi permanent color remains, I have done this and it will not really do much to remove the color only create a hot mess and damage your hair needlessly. If you need to lighten the roots desperately go ahead and bleach just those and continue to try to remove the color with other methods. I have also attempted to color over semi permanent color and this creates an uneven not very nice color with the semi permanent showing through so I don't recommend trying that either.
No mater what you do you will need good conditioning products. You should already be using something similar if you have lightened hair. I use the above products at the moment but I have some more recommendations at the bottom. You need to have a good reconstructing conditioner for damaged hair. I use both Bed Head Urban Antidotes Resurrection and Biolauge Conditioning Balm. Also you need to follow that with a good leave in and oil. I use Paul Mitchell's The Conditioner which is amazing and a bottle last me almost six months and Chi. I use a generic from Sallys and it is the same.
Joico Deep Restore
Bed Head Dumb Blonde Reconstructor
It's a Ten Leave in Spray
Loreal Deep Nourshing Masque.
Morrocan oil drops (many brands)