Is one allowed to take knowledge from internet pages which belong to the people of innovation? If not, then what should I do given that I took most of my knowledge from there? Am I obliged to renew all my knowledge, or is it valid?

All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger.

The basic principle is that the Muslim seeks useful knowledge from scholars who are known for their keenness on following the Sunnah and for glorifying it. If he received sound knowledge from some people of innovation and he verified the soundness of what he learned from them while being cautious of their innovation, then there is no harm in that.

Hence, you should not visit the internet pages of the people of innovation until you are armed with the sound knowledge that protects you from their malicious allegations.

As for what you have learned from them and verified the soundness of by checking it against the statements of the reliable scholars, you do not have to renew it and you may benefit of it.

Allah knows best.