Hi didis_be, welcome to MoI and to the forum!

When you have a question about a particular model, can you please also post the 3DM model file as an attachment instead of only screenshots?

That gives people some objects to work with and try things, and makes it much much easier to give specific suggstions.

But generally it's the Fillet tool that you would use to make a sharp edge to be rounded off.

If you want the whole tip to be rounded and not just the edge, one technique that can work well is to model a rounded cap surface and boolean it with your piece, then use Fillet to round off the edges where the cap hits the main body. Please see this previous post for an example:
http://moi3d.com/forum/index.php?webtag=MOI&msg=2909.2

- Michael