Q:

uninstall mongodb php driver and install a different version

I'm using Ubuntu Xampp (Lampp) and currently on MongoDB 1.5.3 driver.
I need to downgrade to 1.4.5, but when re-installed the downgraded driver, it does not change in phpinfo(). Yes, I have restarted Apache.
So, how do I uninstall the current one and install the downgraded version?

A:

Update: 2018-06-20:
PECL package mongo is now deprecated, you should use mongodb package instead:
sudo pecl install -f mongodb-1.4.4 
Original answer
You can upgrade to a specific version of a driver by using pecl:
sudo pecl install -f mongo-1.4.5
If you get a pecl: command not found error you will need to install PEAR package:
sudo apt-get update && sudo apt-get install php-pear

You can use this command to check that you have the correct version installed:
sudo pecl info mongo

Or you can check php configuration directly with: 
php -i | grep -A 1 MongoDB

