Upgrade from v1.0.2 to v1.0.5

[ToRmEnTeD]

Your Portal Version: v1.0.2
Your phpBB Type: Standard phpBB3
MODs installed: Yes
Your knowledge: Beginner
Boardlink: http://tormented.tv

What have you done before the problem was there?
Had a great time!

What have you already tryed to solve the problem?
Not a darn thing...YET!

Description and Message
I have my board running fine on v1.0.2 but i am wanting to use a couple MODS that i have found that require me to upgrade to the newest version of the portal.
My site if you would be kinds enough to take a look has a custom header and MODS installed as well. I do NOT have any help with this and I'm very much still a beginner. What i am here to ask is if i upgrade my portal will it mess up my forum?
I am using a subsilver2 type style called blackbox_red I have the phpbb gallery installed at least. I would have to recheck to see any other MODS installed.
I am MUCH more worried about messing up the work i have done on the overall_header of my forum and stuff. As this required me bugging the hell out of a lot of people for help....Still begging lol
Anyways, How dangerous to my forum is this upgrade and how much knowledge should i have to attempt the update with MODS and customizations done ?
I guess i made a mistake up top when asked my type of phpbb3 installation...i Picked standard and i guess im using the modded version because i am using the blackbox_red style ?

[Marc]

Make a backup of your board files and your database. If you mess up anything, you can just put the old files and the database backup back in place.