Hi,
Keep the concept and rewrite. Abilities have changed or have been dropped/merged. Spells too. Virtues and flaws have changed a great deal. Spell mastery works differently and is much more interesting. Twilight works a bit differently. And combat... combat changes dramatically every edition. (AM5 is unique in that combat has had a partial rewrite even during the edition!)
You are likely to find that quite a bit stays the same, but a lot also changes.
Anyway,
Ken
If you post what you have, we can help you translate if you are not confident with 5th ed rules.
Bob
It is easier than you may think, yet can be harder too.
Recreate the character using ArM5 rules for post gauntlet magi. I suggest 40xp per year instead of 30, and a season of lab costs 10xp. Don't worry about benchmarks at certain ages. Worry about the end result. Purchase your arts and abilities first, then build your lab, then shove all the lab work at the end. Don't munchkin and make yourself more that what you were. So drop any unused excess.
A number of classic "legacy" spells have been grandfathered in. Others you may have to rewrite up. Most may be okay, but some are quite outside the bouns of current rules. If they are not game breakers, you can always chalk them up to experiment, mysteries, or minor breakthrough.