transom reinforcement.

hi all
im new to this site but very glad i found it! upcoming project should be easier with yall expetrise!
So i got this 12 ft aluminum boat brand Harbercraft..(in canada) i have a 8 hp honda on it but with more then one person it will not plane...
buddy of my gave me a 20 HP merc 2 stroke. Boat is rated for 12hp, So i want to reinforce transom so it can handle extra hp..
I need opinions or what to do to make it stronger,
Thank you

Put strong corners on your transom & cap your transom which will connect to your corners.

We need some pictures of what you have now.
When I replaced my transom I added a 1"x6" oak board to the 1" thick plywood.