Depending on the name, you may not be able to, as there may be no Gaelic version of it. Names can't be 'translated' as such, but are often associated with equivalents in other languages. Many of these equivalents have arisen through translations of the Bible into new languages. In this way the Hebrew name Miriam, for example, has been equated with names including Mary, Marie, Mairi, Màire and many more.
The equation of some Gaelic names with English 'equivalents' is so well-established that many Gaelic speakers use two versions of their first name. In most cases their 'English' name will appear on their birth certificate, but they will use their 'Gaelic' name in Gaelic conversation. This only applies to a relatively small group of names, however, and no Gaelic equivalents exist for the vast majority of names. Some Gaelic names, like 'Eilidh', 'Mairi' or 'Ruairidh' are well-established 'in English'.
For more information, you can consult the book 'Ainmean Chloinne: Scottish Gaelic names for children', from the publisher Taigh na Teud, available from www.gaelicbooks.net.