This will depend on your child, and the exact reasons for not wanting pullup nappies. So the first thing I'd try is find out more about why she does not like the pullup nappies. Don't settle for "I don't like the pullup nappies". Instead, sit her down when she is relaxed and in a good mood, explain to her why you want to change to pullup nappies, and listen to what she objects to.
A 2.5 year old should be able to explain a bit what the problem is. Maybe they are too tight? Or maybe she liked the pictures on the old ones better? Or maybe she's afraid she will have to do without nappies soon (as skymningen suggested in a comment)? Try to find out.
To support the change, you could point out advantages of the new nappies to her:
- She can more easily take off/put on the nappies herself - independence is important for most toddlers.
- She can choose nappies with pictures she likes (if such are available in stores).
- The nappies are for big children, and she's a big child now.
- They will not come loose as easily as the old nappies.
Also, offer to try out the new nappies together with her. Show her how they are comfortable and easier to put on, and again, listen to complaints she may have.
Of course, if you cannot persuade her, you may need to put your foot down, and introduce some consequences. For example, longer outings (such as going to the zoo) are no longer possible because the old nappies don't last long enough.
As usual, whether, when and how to escalate in that direction is up to you. If using regular nappies causes few real problems, I personally probably would not bother in most cases; if there are real issues, such as problems during outings due to leaking nappies or similar, things can be different.