Do you have a skywards membership? If so you can buy the skywards miles and then use it to upgrade that leg. From your post it looks as if you dont have any status with emirates. If you have a friend/family member who has a skywards account with miles you can ask them to upgrade the ticket for you.Even if they have to buy some miles it might be cheaper than cash.

LIS-DXB-BNE costs 62500 miles and DXB-BNE costs 45000 miles for upgrading from a flex business to first.

You will earn 31500 miles as a skywards blue ( lowest tier) for the LIS-DXB-BNE return in flex J for the ticket that you paid for.

Do not try to transfer miles from one account to another as there is a transfer fee.