The problem with upgrading an older bike like this is that once you accept that you need one part you sort of have to upgrade the whole package. This is the reality that the folks above are giving you in pieces.

Before you start figure out what you'll need and add it all up. You may well find that it's as cheap or only slightly more expensive to just buy a used but decently current tri bike than to upgrade this old warrior.

After all so far you're looking at;

• new bars and shifters
• likely you'll want aero brake levers instead of the old flying housing levers
• tri bars to replace the old drop bars
• the indexing bar end shifters
• new wheels and cassete to go with the shifters
• cold forming the old frame to adjust the dropouts to accept the new wheel
• and likely a new rear derailleur to go with the index shifters

All of this is going to set you back a pretty penny. Add it up and see if you really want to put that much into the old Centurion or if you'd rather just buy a newer used tri bike and not need to buy all this other stuff along with installing it.