hi,

see the eligibility criteria of upsc civil service exam is candidates from any of the education back ground who holds a bachelor degree in any discipline are eligible to appear in upsc civil service exam. however candidates must have the age criteria . for general category age limit is     21 to 32 years. as for 2020 notifications the candidate should have completed 21 years as on 1st August 2020 (for the UPSC CSE 2020) and not completed 32 years as on 1st August 2020 i.e., he must have been born not earlier than 2nd August, 1988 and not later than 1st August 1999. age relaxation is applicable to reserved category candidates.

now coming to the syllabus of upsc , syllabus is quite unique and the course can be prepared by any of the background students.

now coming to b.a political science and b.a in sociology both of the course is of three years duration, but the course syllabus is different.

b.a in political science syllabus includes  historical and modern political systems, public administration, governmental policies and procedures, international relations, and public affairs.

b.a in sociology syllabus includes the study of culture, social interaction, social stratification and social relations.

so whatever course you may take it would not be very much related with upsc syllabus. so choose the courses as per your interest and try to get admission in tier 1 college.

upsc civil service exam has two stage , prelims and main. you may follow the below link to know about the full syllabus,

https://competition.careers360.com/articles/upsc-ias-syllabus