someone hacked my email, will changing my password stop them?

Wouldn't hurt. Plus ... you better change it before they do. Then you can't get in.

no

This is how to secure a hacked account: https://help.yahoo.com/kb/SLN3516.html

First, you, or anyone else, might receive an email in the inbox with
your email address as the From name. Anyone can use your
email address as their From name and this does not mean
that your email account has been hacked. You, or they, can
check this by hovering the pointer over this From name(your
email address) and it will usually display the actual address it
is coming from. if it indicates a different email address delete
it. If the email is spammed it will stop your actual emails from
being received in the Inbox should you send one to yourself.
Just delete this message. Otherwise, see below
=======================================
How can you tell if your account has been hacked
https://help.yahoo.com/kb/yahoo-account/SLN2090.html?impressions=true
====================
SECURING A HACKED ACCOUNT
https://help.yahoo.com/kb/mail/SLN3516.html?impressions=true
====================
REPORT A HACKED ACCOUNT TO YAHOO
https://help.yahoo.com/kb/SLN3402.html?impressions=true
=======================================...
In case you are not aware unless
you choose a Best Answer no one will get credit for
answering it....so.....Please
once your question has been posted for at least 1 hour
and has at least one good answer return to the Yahoo
question/answer site. Click on your Avatar(photo) Your
questions should be displayed. Click on this question
and then click on AWARD BEST ANSWER below
your chosen answer, give it a star rating....then click
on SUBMIT.
Many thanks from all of us out here.
=======================================