UC might be difficult to transfer into depending on your GPA and total units taken so far. Most UCs right now do not take students with more than about 80 - 90 units (different for each UC) if you have any 4year credits in the mix. This max unit disqualification for transfer students with 4year credits may go away, but for now it is in place. So if you are approaching the 80 unit mark, be aware of that.
Secondly, UCs admit mostly based on GPA. If you are a 2.5 overall, I have a hard time imagining you getting into a UC, even a Merced/Riverside. For example, UCLA average admit had a 3.7 last year. Profile of Admitted Transfer Students, Fall 2012 - UCLA Undergraduate Admissions
You would have a more realistic chance at a CSU, especially if you took a year of CCC classes to bring your GPA up first.
Many of the UCs and CSUs post their transfer GPA thresholds--you just need to get busy with a search engine. Try words such as "gpa" "transfer" "impaction" along with the college's name. To find the UCLA link I included above I just typed in "ucla transfer gpa"--it isn't that hard, just takes a little bit of leg work and trying different combination of buzz words to find these stats.
Btw - you can NOT apply as a freshman and pretend you don't have two years of credits already. There are clearing houses that colleges can look at to see if you already have been in college. And even if you manage to slide in as a freshman because of poor record checking, if you get caught some years later (even AFTER graduating) you can have your diploma rescinded for lying. Don't do it.