Upgrading to a first class [closed]

In general no. You might be able to cancel both and use these monies to buy a first class ticket. Or you might not, depending on the tickets you bought. Read the email it came with. It is a tried and true tactic (I did it for example) to buy two tickets for yourself (or perhaps yourself and your musical instrument) because it's comfortable enough and yet still way cheaper than business (at least on transoceanic flights this is typically the case) so you can't expect the airline to give you a (much) more expensive ticket in place of two cheaper.

Probably not.

In general 2 economy class tickets will not cover a single first class ticket.

You might try a business class ticket instead.