To do so, take the following steps:

How to recover an Opportunity?

Go to ‘Oportunities’ tab and click ‘Advanced search’;

Inside the ‘Advanced search’ menu, on the ‘Stage’ dropdown menu, select ‘Deleted’ and click ‘Search opportunities’.

All deleted opportunities will be shown.
To recover an opportunity, open it;

Within the opportunity register click ‘Recover’.
After this, the opportunity will be recovered.

How to recover a Lead?

Go to ‘Leads´ tab and click ‘Advanced search’;

Inside the ‘Advanced search’ menu, on the ‘Stage’ dropdown menu, select ‘Deleted’ and click ‘Search Leads’;

All deleted Leads will be shown.
To recover a Lead, open it;

Within the Lead register, you can promote it again to ‘Opportunity’ or definitely delete it.