I want to change a hot water baseboard heater what is the steps imust take thanks

Turn off boiler power.
Secure fill valve and Drain boiler water.
Remove old section of baseboard.
Replace with new.

NOTE if you do not replace a section you will have to see how it is piped. Many times baseboard is piped to more than one piece. If you do not reconnect the two lines for the old heater the others may not work .

Note if they are not piped to different and this board has its own feed then you can probably cap it off.

You might have to have someone that knows what they are doing check to see how your system is piped.

Refill boiler and bleed air out of system.

Turn on and check for proper operation.

I am sure I am missing a item or two but this is the basics.