update linq to sql with variable names?

im pretty much a beginner to using ASP.net and linq to sql but what im trying to do is update a column of a table based on a variable. at the momment i have

Dim db As New sqldcDataContext
 Dim update As tableName = (From i in db.tableNames _ Select i)
 

i think this selects everything, how could i have two variables, one to store what table to update and the other what column. is this possible?

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