[TheLastSuperman]

Yes vBulletin Solutions does offer an upgrade service .

1) Please login first at https://members.vbulletin.com and then click on "Purchase" in the top navigation. If you have not purchased yet you can add these "add-ons" while addint other items to cart etc etc.
2) From there click on "Get Add-Ons" at the bottom. Here is the page link - https://www.vbulletin.com/addons.html
3) Select the license your associating the "add-on" with and yes that includes services such as a site install/upgrade.
4) Now select the service which is "Professional Installation/Upgrade"

*Please note the description:
"Professional Install/Upgrade only includes vanilla install with no customization"

So with that being stated ^ I can tell you that if you're running a custom style on your vBulletin 3 or 4 forum you will need to remake it in 5.x format, also custom modifications will need to be reviewed as well. If you do want to purchase 5.x then I suggest doing so and setting up a clone of your current live site and testing the upgrade and preparing the style/other before you plan the actual live site upgrade that way you can sort any and all issues if any arise far far ahead of time .