Possible or not?

[camlearner]

I have an application installed. It has a textbox in this application formatted with Font Size 10. It is possible to change this textbox to font size 15 or not because this application already compiled.

[Hack]

Do you have access to the source code?

[camlearner]

No, i don't have.

[dglienna]

Then probably not. If you could change the text size, you'd also have to change the size of the textbox, and possibly have to move it around the form.
What problem are you having, exactly?

[Hack]

No, i don't have.

Then you aren't going to be able to do much with it.

If this is a piece of software that your company purchased, do you have a contract with the vendor? Maybe they could build in a feature to permit that for their next release.