Hi @lessariasaa for the power up, you can do it as in this image here

there is the power up option there and you click that for power up your liquid steem.
And for power down which is changing your Steem power back to liquid steem, you can do as in the photo below

Congrats! You have sufficient knowledge on basic security on steem and now ready for Achievement 3 task here https://steemit.com/hive-172186/@cryptokannon/achievement-3-mentor-by-cryptokannon-content-etiquette

See you soon! 😊