How to update some records in mssql

In certain conditions, we want to update some records, not all data. Suppose we want to update the first 100 data from a query. How to do it in MSSQL??.
The following query should be executed:

update top (100) table1 set field1 = 1

Notes
Make sure you replace "table1" with the actual table name.
And replace the field1, with your column names.