You should start by reading some of the guides on the Pensions Authority website to understand things better. And then read some of the existing threads here about pensions. For example:
Pension arrangements generally allow you to transfer your pension benefits from one arrangement to another. The transfer rules depend on the arrangement you are transferring from and the arrangement you are transferring to.
Even even "merging" pensions is possible it's not necessarily a no brainer to do so as there are pros (e.g. simpler administration, lower charges etc.) and cons (e.g. "fragmented" pensions may offer flexibility that a "consolidated" one does not, higher charges etc.).