Okay so I haven't logged into Sylestia since December or so and so after I logged in yesterday, I noticed some of the updates on Sylestia, which is great and all but now I'm confused on how everything works, not to mention, I can't change the HP or the Strength or Intelligence on my syleties anymore so can someone please explain?

There has been quite a lot of changes recently, so things can take a while to get used to again.

The reason why you can't change the stats of your pets is because the level up/proficiency system has been changed, and pets now need to be attuned to an element, before their stats can be customised. When you choose an element, and add to strength/intelligence, the stat that the element uses will be the one that'll be increased, so you can't choose to add both strength and intelligence now. Also, "level-up points" have been removed, and the pet will have increase in all stats as they level up now.

Here's a thread announcing the change to the system: https://www.sylestia.com/forums/?thread=44190

Also, you can click on the ? on the pet's proficiency page to read more about how the proficiency system works now.

Same, I came back from a hiatus for around the same time as you!
I'm a bit acquainted with the new update but not entirely, so here's a short summary:

1. The proficiency trees for pets were updated. There's no more level up points to distribute, and points are automatically added to pets as they level up (someone told me that, not sure if that's the case).

2. Proficiency customization for pets changed. You first have to "attune" your pet to an element before being able to put points in. It's like the previous system but broken into 2 steps.

3. The trees' elements and their attacks didn't change, but the lvl25 attack from before the update is now available at lvl0 (such as Fireball).

4. The distribution of points is different. Instead of getting 1 every 5 levels, you get 1 at lvl0, lvl30, and lvl60. The rest are capped until the mega zone comes. So at lvl60, you can have a max of 3 points to distribute.

(You also don't need to distribute the first point you get to be able to use the old lvl25 ability. It's open to you at lvl0. It's neat that you can assign a point starting from lvl0 too!)

5. You can only distribute them over the 4 stat increases. Strength and intelligence got lumped together, and the kind of physical/magical damage you deal depends on the tree you attune to (you can hover over the stat to see which trees do which).
So you can only put points in HP, Str/Int, Dex, and Agi.

6. You don't have to put points in specific attacks. The mechanic to rank them up is disabled until the mega zone is released.

Knowing those things helped me get up to speed a bit. If you follow the battle party guides here where they tell you to make tanks and glass cannons, the builds are pretty much the same.
(assuming you use lvl60 pets) Tanks usually have 3 points in HP. Glass cannons usually have 2 points in str/int and 1 in dex OR 3 str/int.

Also:

7. Equipment that drops post-update is slightly tweaked. The update page explains it better, but equipment values will differ slightly than before. It's somewhat useful to know if you're keen on stats.

Hope these help!

Thank you for the acknowledgement that really helped a lot :)