How to commit the rest of the transactions of an update in large bulk?

I have to modify the table structure where the table have a lot of data already. The log is getting full due to uncommitted transactions, there is a lot of data being updated in large bulks, not all of the transactions are committed, the update task cannot be completed.
However, there is no more spare disk space for it to commit the transaction. Anyone can help?what exactly are you dong? bulk insert?|||change some field 's size and its predefined function where the table have about 50,000 data already.