UPDATE Records In 1 Table With Result Of Select Statement

I want to update records in 1 table with the result of a select statement.

The table is called 'MPR_Portfolio_Transactions' and contains the following fields:

[PTR_SEQUENCE]
,[PTR_DATE]
,[PTR_SYMBOL]
,[PTR_QUANTITY]
,[PTR_ACUM]

And the select statement is like this:

SELECT SUM(PTR_QUANTITY) OVER (PARTITION BY PTR_SYMBOL ORDER BY PTR_DATE, PTR_SEQUENCE) AS 'ACUMULADO'
FROM MPR_portfolio_transactions
ORDER BY PTR_SYMBOL, PTR_DATE, PTR_SEQUENCE

This select statement generates one line per existing record. And what I would like to do next is to UPDATE the field 'PTR_ACUM' with the result of the 'ACUMULADO'

the key is PTR_SEQUENCE