To use an If then else formula you need to tell it what the alternative is for a false return.Something like  If {table.field1} = "7" then "5"
                                                    else {table.field1};
                                               If {table.field2} = "7" then "6"
                                                    else {table.field2};
                                               If {table.field3} = "7" then "7"
                                                    else {table.field3};
                                               If {table.field4} = "7" then "8"
                                                    else {table.field4}

Try substituting "and" for the " ; "