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 is His slave and Messenger.
You are not sinful for browsing and downloading useful sites or books, even if they contain slogans that violate the Sharee'ah.
If it is possible to change such slogans after downloading the material, then you have to change them because ‘Imran ibn Hittaan narrated from 'Aa'ishah that the Messenger of Allah never left in his house anything containing the figure of a cross without destroying it. [Abu Daawood]
Allah knows best.