Can I change type of current master node

We have 3 nodes of elastic search all nodes is mater=true and data=true. When we try to find the best practice almost is recommend to setup 1 node for master=true,data=false and another 2 nodes is master=false,data=true. So if we need to change it how going on with current master node. It will be automatic allocation? or we have to delete and insert data again?

For another question Do you have any configuration suggestion detail is bellow

Hard ward for all nodes
CPU 3.4 8 core
Ram 32 GB
HDD raid 0 1TB
Current heap size 18GB
Elasticsearch Data 160GB | 108,190,284 records