Have you tried:

-> Unfavouriting the item
-> Smelting the item
-> Leveling up Yoshitsune more

A high leveled player made an Excalibur for me, ATK 208-305 but I can't update it anymore. When I try to, it's locked. How can I upgrade/enchance it again?

You need to smelt it with another Excalibur before you can increase it's enhancement level. You have to do this every 10 levels.

I will smelt it with another excalibur but as material I only need to use that right? And do I need to use things such as 5% chance more and other extra stuff?

Heretic wrote:I will smelt it with another excalibur but as material I only need to use that right? And do I need to use things such as 5% chance more and other extra stuff?

Use the options you want :)

I generally go for grade up and skill evo (unless I'm using skill cards or the skills I want are ranked 5). Skill change can also be good.

I tried to smelt my Excalibur that I can't enchance/upgarde too, it is locked. It is level 50 and my game level is 26. Is it because of that? When can I unlock it again? Do I need to level up friendship with Yoshitsune? My friendship level with Yoshitsune is at LVL 10.

Yeah the game tells you that Yoshi's level is too low to smelt beyond 50. You need to progress the story quests then feed her friendship items.

Anyway, +50 weapons should be fine for the lower levels, wouldnt waste money and time smelting past that till you are level 60+ as you will out level the weapon way too fast for it to be of any lasting purpose.

Well, I'm lvl 27 at the moment.
So which kind of frienship I need with Yoshitsune? I think I'll just let it like that for now.