During the sprint can anyone change the scope of sprint backlog?

You haven't mentioned the Sprint Goal. Should that have a bearing on how the scope of work might emerge?

You mix PBI and tasks somewhat interchangeably.  From my perspective PBIs are not tasks.  Tasks are the things you do in order to satisfy a Product Backlog Item that has been pulled into a Sprint Backlog.  So adding/removing tasks is something I would expect to happen as the Sprint Backlog Item [SPI] (formerly a Product Backlog Item) is worked and new information uncovered. 

As for adding/removing (S/P)BIs, @Ian's question comes into play.  Yes, you are correct that this should occur in conjunction with discussions between Development Team, Product Owner and Scrum Master.  (I include Scrum Master because the entire Scrum Team has played a part in crafting of the Sprint Goal). Those conversations should be focused on how these changes impact the Sprint Goal.  It is not wrong to make changes that negatively impact the Sprint Goal as long as it is known and everyone fully understands the impact.  But none of those decisions should be made unilaterally.  These same rules apply if the Product Owner is the one wanting to change the Sprint Backlog. Since the Development Team are the only ones that can change the Sprint Backlog, the Product Owner must work through them.  But the respect that everyone has for each other will lead the team to make decisions that can be accepted by everyone involved.

Thanks Daniel, you cleared my doubt.

I understand evolving the tasks is completely fine on sprint backlog and yes PBI and tasks are two different things.

My doubt was on scope of sprint ( little confused about difference between scope and goal though!), my understanding is, even a PBI can also be added or removed with mutual understanding (team and PO) as you also mentioned withing a sprint.

So in summary, you can change scope of sprint ( task level as well as PBI level) with due considerations and mutual agreements.

Is the message received correctly Daniel?

The Development team owns the Sprint Backlog, and therefore (only) the Development Team should change it during the Sprint (based on the outcomes of the Daily Scrums) towards meeting the Sprint Goal. Keep in mind: the Sprint Goal is agreed on and fixed, the way to get there (Sprint Backlog) is not fixed and only a forecast of work needed to meet this Sprint Goal.

It is of course advised, for Transparency, to at least keep the PO up to date on these changes, but preferably collaborate with the PO!