Biological process

up regulation of T-helper cell differentiation, up-regulation of T-helper cell differentiation, upregulation of T-helper cell differentiation

Any process that activates or increases the frequency, rate or extent of T-helper cell differentiation.

positive regulation of T-helper cell development

Note that immunologists typically use the word 'development' to refer to cells of B or T cell lineages undergoing the process that GO describes as 'cell differentiation'.