What is the top lev I can get to? My character are lev 22 . Thinking to chang bart to fighter am I to late to build a good fighter.

The max level is said to be 50. But you surely won't reach it in a normal game.
Normal level at end of game is ~25, i think (more for first game, or with smaller parties).

My fighter/bishop duo has IIRC 160 million experience, and is level 38/34. Since there seem to be no monsters with level >40, advancing to level 50 will take a very very long time.

Level 22 is pretty late to be switching, but not unheard of: your bard will still play instruments at his current level/music skill.

But I'd save the game before switching, just in case you don't like the result. it may be worth it, if you have a really good weapon thats otherwise going to waste, but unless he already has a pretty good skill in that weapon category, it'll take a while to get it to a good level.

In W7, a switch late in the game could allow you to jump several levels [with the attendent, though random bonuses for each] in the course of a single combat. W8 doesn't work that way: your character will be a level 22 bard, level 1 fighter, but next level is pretty much as far away as if you hadn't switched [some classes level faster than others, I think fighters are among the fastest, but dunno about bards].

In my first game, I switched some characters around 20, and it was worth it. They, however, were special cases: my valk wasn't going to access upper level priest spells, for instance, so I made her a fighter to allow her to use some item or another she couldn't have had otherwise. Worked out ok, since most of her attributes [strength, dex, etc.] applied equally to both.

Oru

For Bards, Level 18 is my suggested level (max level for using ALL instruments in game), or whenever you feel comfortable with their Music skill because at Skill 75+, you can't improve it via skill points acquired by Level ups. I made the switch when my Bard was Level 18, and she had 100 skill.