To do this, you must complete the first quest in the game, [The Den of Evil], by clearing the eponymous Den of Evil dungeon of all the monsters dwelling therein. Once done, talk to Akara in the Rogue Encampment and she’ll reward you with +1 Skill Point to distribute freely and a one-time option to respec your character. You do not have to respec immediately, you can save this respec for as long as you wish. You can complete this quest in all three difficulties - Normal, Nightmare and Hell - meaning a single character can earn three opportunities to respec over their career.
This is actually quite generous, as it allows you to, say, make a build suited for new characters to rush themselves through Normal/Nightmare, but which are less suited for Hell difficulty. Once they’ve progress as far as they can reasonably or easily go, you can respec into a more proper Hell-oriented build. Hence the suggestion of Beginner Builds in this guide, which are designed to get you off to a good start rather than to be competitive in Hell difficulty. It’s just a sad fact that since some skills have a level requirement, the best builds aren’t available right out the gate, and waiting for a Lv30+ skill to unlock isn’t the best way to progress through Normal difficulty.
This also allows you to dump points into Strength to wear whatever gear you find, knowing full well that some rare, powerful, lower-Strength alternatives exist. You can’t rely on RNG giving you the drops you need when you need them; boost that Strength up high enough to use a Spirit Monarch and if you find a different/better shield you’d rather use, or enough runes to make the runeword [Enigma], you can respec and assign your Stat Points elsewhere. Better to have a less-than-perfect build that’s serviceable with the gear you currently possess than to let the perfect be the enemy of the good; while a flawed character is out there more easily clearing areas and killing bosses and getting new/better gear, the dainty, Strength-starved toon will be struggling.
Or, you could just be incredibly lucky and end up getting an incredibly rare, powerful, build-defining drop that behooves you to switch gears entirely. It’s rare (there’s not a whole lot of items that, once obtained, beg for a character to be built around them - but they arguably do exist), but you’ve got three respecs, so switching your Meteorb Sorceress into a [Lightning] build, or rolling a [Bowazon] to use that new [Windforce] you found… well, it’s a nice dream, anyways, and possible thanks to the ability to respec.
Finally, it’s worth noting that once you’re established, rolling a new character isn’t that difficult. A few hours and some hand-me-down gear and you’ll be ready to go. It’s not all that hard for an experienced player to reach the end of Hell difficulty and raise a new character up to Lv80. It’s fine to get attached to a toon, but it’s not always a bad idea to just make a new one if the need arises.