I Want To Delete Avast! but it wont let me im tired of having a bunch of viruses and i want to reinstall windows defender but avast will not allow me to delete it it has so many roots in my harddrive its like a plague help me please. 
Download the uninstall utility from here. Open the utility and select OK or Yes all the way through the process.
How are you trying to delete avast ?
It should be able to be removed in the normal control panel - Add Remove Programs or Programs & Features, like any normal program. Have you tried that, if so what happened ?
Why won’t it allow you to do it, e.g. what error messages are displayed ?
If, as you say, there are that many viruses and rootkits, etc., The first thing I would do is create a topic in the viruses and worms section and follow the instructions given in the following topic.