LastPass - How Do I Change a Site Password in LastPass?
To keep up with best security practices, it is recommended that you update your passwords regularly to minimize security compromises. First, change your password directly on your desired website within the website's settings, then LastPass will prompt you to update your stored password within your Vault. For further instructions refer to the LastPass support article: Change Site Password.
For advice on creating strong and memorable passwords refer to this KB article: LastPass- How to create a strong and memorable password.
Alternatively, instead of manually creating new passwords, you can use LastPass to generate secure passwords by following these instructions: Change an Old Password to a New, Generated Password.