Inexperienced GMs worrying about balancing higher-level wizards is a recurring theme in fantasy gaming discussions. Whether this is necessary or useful is a topic of endless debate, as are the methods to accomplish the task. Some of the methods GMs have tried are extraordinarily complicated, such as raising the levels of individual spells. Luckily, there are some very simple tricks to give your non-wizards an edge if you need to do that.
If wizard characters are dominating your game, place more magic weapons, magic armor, and items which benefit physical attribute scores into treasure recovered by the party.
Many adventures feature stat boosts as rewards. Place a stat boost feature into one of your dungeons or stories which affects Strength. This will reward melee fighters much more than magic users. You could also boost Dexterity and Constitution, but those also reward magic users.
Throw golems and other magic-immune (or magic-resistant) foes at your players on a regular basis. Your wizards will feel much more reliant on the party fighters.
Encounters Per Day
Wizards are best when the number of encounters per day is very low. Throw more encounters per day at your players to highlight the advantages of non-casters.
Even better, throw monsters at the party while they are sleeping to prevent casters from recovering spells.
These can be too heavy handed and should only be used in extreme situations. If you need to do this, your players likely have larger issues.