We have found one software suitable in our database for this conversion.
3g2 to 3ga conversion is actually not needed, since both files are in the very same 3GP format, with just different file endings to distinguish between the content. You can just rename the suffix if you want, but 3ga is used for audio files only.
Of course some multimedia converters will claim to support this conversion, but really they will just rename it.
3G2
A 3g2 file extension is commonly used for files that use 3GPP2 multimedia file format to store audio and video data. A 3GPP2 format is based on the MPEG-4 standard.
3GA
Files with 3ga extension are audio files stored in 3GPP multimedia file format. 3GPP file format was developed for 3G and UMTS mobile networks multimedia services. 3GPP is supported by variety of mobile producers, such as Nokia, Samsung etc. 3GA file extension identifies only audio stream stored in 3GPP multimedia container. Audio stream can use AMR-NB, AMR-WB, AMR-WB+, AAC-LC, HE-AAC v1 or Enhanced aacPlus (HE-AAC v2) audio codecs.