How to turn on GTID on MariaDB if already using binary/position replication?

Question

MariaDB 10.3

current master config

[mysqld]
log-bin
server_id=1
binlog-format=mixed
expire_logs_days=10

current slave config

[mysqld]
log-bin
server_id=2
binlog-format=mixed
expire_logs_days=10

I can stop both master and slave if needed for changing replication method.

So questions are:

1. Do I need to stop replication and application and then execute "CHANGE MASTER TO MASTER_USE_GTID = slave_pos" Is it enough? Should I purge bin logs?
2. If so how do slave knows about where master server is?
3. Should I changed binlog-format to "row"?