If ALL your text data is less than 8000 bytes per record, then you could
select replace(Convert(VarChar(8000), comments), '"', '"')
from tblcaseinfo
where PatIndex('%"%', comments) <> 0
Notice PATINDEX for your search condition.
If it's longer, then you have to use UPDATETEXT. see BOL.
Once you understand the BITs, all the pieces come together 