The most common way is to use a trigger punch or puller. This tool helps to remove the old trigger and pins from the lower receiver.
The next step is to insert the new trigger into the lower receiver. Make sure that it is in the correct position before you start to pin it in place. You will need to use a hammer and brass punch to secure it in place. Avoid using a steel punch because it can cause damage to the new trigger.
The final step is to reattach the pins and test out your new trigger. Make sure that it feels comfortable and functions properly before you take your rifle out for a test run.
If you are not comfortable doing this installation yourself, you can always take it to a qualified gunsmith. They will be able to install it for you and make sure that everything is working correctly.