As you open your Snapchat account and feel like someone else has used your account before you, then you should change your password immediately, before the hacker does. To change your Snapchat account password, you have to do is:
Go to your Snapchat login page and click on the forgot button
Then, enter your phone number or email account, to which link will be sent to you
Then, tap on the link to change your password.
After then, you can reset your new password on Snapchat and save your Snapchat from getting hacked.