The main tools for computing the radius of convergence are the ratio test and the root test.
In particular,
If $\displaystyle L = \lim_{n\to\infty}\left | \frac{a_{n+1}}{a_n} \right |$ or $\displaystyle L=\lim_{n\to\infty} |a_n|^{1/n},$ then the radius of convergence is $\displaystyle\frac{1}{L}$.
The endpoints of the interval of convergence have to be checked separately, as the root and ratio tests are inconclusive there. Here other methods for convergence should be used, such as the $p$-series, alternating series, comparison tests, the integral test, or the divergence test.