Do note that there is specific queue system in the Library for this purpose but sometimes it may fail to work as expected.Try canceling all the other download queues and restart Steam.
There can be another conflict between your internet connection and your disk write speed.
If there are more than one download/update queues present in your Steam library, you should cancel them and try to update/download only one game at a time.
This is very important as your Steam client can get overwhelmed by a number of requests it has to process.
The game may be stuck as “queued” or may be downloading at 0 Bytes per second.
This problem can occur due to many different reasons.
Steam has divided its services into different geographical regions.